The Missing Dollar Riddle

The well-known “Missing Dollar” puzzle! It’s fun because it smartly tricks our minds. Let us take it one step at a time:

The Riddle:

Three friends go out for lunch and spend $30. Each person contributes $10, so they pay $30 in total. The waiter realizes that the bill was only $25, so he gives back $5 to the friends.

Since $5 is hard to split evenly among three people, the friends decide to tip the waiter $2 and split the remaining $3, taking $1 each. Now, each friend has effectively paid $9 ($10 initially paid minus $1 returned).

Here comes the mystery:

  • Each friend paid $9.
  • $9 × 3 = $27.
  • Add the $2 tip, and you get $29.

But the friends started with $30. Where did the missing dollar go?


Breaking it down:

The riddle plays a clever trick on our logic by misdirecting the calculation. Let’s analyze the scenario step by step.

Step 1: The total money paid

The friends originally paid $30. Out of this:

  • $25 went to pay the bill.
  • $2 went as a tip.
  • $3 was returned to the friends ($1 each).

This accounts for the entire $30:

Step 2: Where the $27 comes from?

When we say that each friend paid $9, we’re effectively combining:

  • The $25 bill, which is part of what they paid.
  • The $2 tip, which is also part of what they paid.

So, the $27 already includes the tip:

Step 3: The trick

The riddle’s trick lies in the misdirection. It incorrectly adds the $2 tip to the $27 (the total paid) instead of properly accounting for where the money went. The tip is already part of the $27! There’s no missing dollar — it’s all accounted for.

The Conclusion:

The “missing dollar” doesn’t exist. The confusion arises because the riddle mixes two separate concepts: the total amount spent ($27, including the tip) and the original $30 contributed. By carefully tracing where each dollar goes, we see that the money is accounted for perfectly.

Why this riddle is so fun?

The Missing Dollar Riddle is a great example of how math can trick us when we’re not careful. It reminds us to always pay attention to what is being added or subtracted and why. It’s not just about numbers—it’s about logic and clarity.

Do you know someone who’d enjoy solving this riddle? Share it with them and see if they can figure it out before reading the explanation!

Happy riddling!

January 21 – Planetary parade

A planetary alignment is a spectacular celestial phenomenon in which planets appear to line up in the sky from our vantage point on Earth. Although the planets are still far away in space, their locations provide a visible alignment that fascinates stargazers and astronomers.

Today’s Planetary Alignment (January 21, 2025)

Tonight, six planets—Venus, Mars, Jupiter, Saturn, Uranus, and Neptune—will align in the night sky.

Visible Planets

Naked Eye: Venus, Mars, Jupiter, Saturn.

With Telescope/Binoculars: Uranus and Neptune.

Best Viewing Time

Shortly after sunset until around 9:30 PM.

Location and Tips

Look towards the western sky.

Choose a dark, clear location with minimal light pollution.

Happy Stargazing!

June 3 – Planetary lineup

On June 3, 2024, a spectacular planetary alignment will be visible from various parts of the world, including India. This rare celestial event will feature six planets: Jupiter, Mercury, Mars, Saturn, Uranus, and Neptune, appearing in a line across the sky.

In India, you can witness this “parade of planets” just before dawn. To get the best view, find a spot with a clear view of the horizon and minimal light pollution. Most of the planets will be visible to the naked eye, with Saturn and Mars being particularly easy to spot due to their brightness and distinctive colors. Uranus and Neptune will require a telescope for better viewing due to their distance and faintness .

So, mark your calendars and set your alarms early to enjoy this extraordinary alignment. Happy stargazing!

Circle: A 360° story

Have you ever wondered why there are 360 degrees in a circle?

We’ll explore the practical reasons and fascinating history behind the circle having 360 degrees as its angle.

Understanding the origin

Sumerians and Babylonians

The Sumerians, an advanced civilization that flourished in the third millennium BC, were the ones who first developed this concept. Ancient civilizations like the Sumerians and Babylonians used the base-60 numeric system, which has a historical explanation. This method influenced the circle to have a 360-degree angle. Because of this decision, angular measurements were easy to use in their astronomical and mathematical computations.

Greeks

The Babylonians may have inspired the Greeks to divide a circle into 360 degrees. Based on their base-60 numeric system, the Babylonians chose 360 degrees in a circle. Historical evidence implies that the Greeks adopted this angle division from Babylonian mathematics.

Hipparchus, a Greek astronomer and mathematician, played a crucial role in the adoption of the 360-degree circle. His work in trigonometry and astronomy contributed to the refinement of angular measurements, paving the way for the widespread acceptance of 360 degrees in circles.

Mathematical Significance:

If you think about why people use 360 degrees to depict a whole circle instead of using 100 or 1000, it looks easy to have 100 or 1000. However, in reality, it is the optimal solution. A numerical value such as 10 or 100 would have been mathematically more inconvenient.

✍One of the key reasons for choosing 360 degrees is its divisibility. Unlike other numbers, 360 has numerous divisors, making it ideal for dividing circles into equal parts. This practicality extends to various geometric and trigonometric calculations, making the 360-degree system a cornerstone of mathematical precision.

For all positive integers up to 360, 360 has the maximum number of divisors. whereas 100, which many of us would like to see as the value of the complete circle, has a total of just nine divisors. The number 360 is called a highly composite number because it has more divisors than any smaller positive integer. It’s a handy choice for calculations because of this property.

360 has many divisors, making it easy to divide a circle into equal parts.

Dividing 360 by 2, 3, 4, and 8 gives the whole numbers, 180, 120, 90, and 45, in that order. On the other hand, dividing 100 by 3 and 8 gives 33.3 and 12.5 as decimal numbers, which makes calculations difficult.

Understanding the rationale behind dividing a circle into 360 degrees and the advantages it offers in various calculations is crucial. The divisibility of 360, along with its historical and practical significance, makes it a preferred choice in mathematics, science, engineering, and navigation. However, exploring alternative systems and understanding their implications can broaden our perspective and enhance our mathematical reasoning. Ultimately, the 360-degree circle serves as a fundamental concept that bridges theoretical knowledge with practical applications, highlighting the beauty and utility of mathematical principles in our everyday lives.

Wind chill Temperature (‘Feels like’)

Ever noticed the “feels like” term in your weather app?

Your Weather app forecasts high, low, and “feels-like” temperatures.

The “feels like” temperature is helpful because it gives a more accurate representation of what it will feel like when you step outside, beyond just the recorded air temperature. It’s a useful metric for individuals to better prepare for the weather and dress accordingly.

The feels-like values are not just randomly predicted numbers but are calculated by considering certain factors using the wind chill formula.

In 1945, Paul Allman Siple and Charles F. Passel created the wind chill formula that is currently in use in the United States and Canada. They conducted experiments with human subjects to understand how wind and temperature interact to influence perceived coldness. The formula has undergone revisions over the years, and the current version is based on their initial work.

The wind chill formula is used to calculate the wind chill temperature, which is the perceived temperature felt on exposed skin due to the combined effects of the actual air temperature and wind speed.

WCT = 35.74 + 0.6215 X T – 35.74 X V0.16 + 0.4275 X T X V0.16

  • T stands for temperature, and V stands for wind speed.
  • WCT is the wind chill temperature in Fahrenheit.

In summary, the formula helps to estimate how wind and temperature interact, providing a more accurate representation of the perceived coldness in windy conditions.

For temperatures in Celsius, a different formula is used. The formula for the Wind Chill Temperature (WCT) index in Celsius is:

WCT = 13.12 + 0.6215 X T – 11.37 V0.16 + 0.3965 X T X V0.16

  • T stands for temperature, and V stands for wind speed.
  • WCT is the wind chill temperature in Celsius.

Again, it’s important to note that different countries and meteorological agencies may use slightly different formulas or criteria for calculating wind chill, so variations may exist in different regions.

National Mathematics Day

Srinivasa Ramanujan, often referred to as Ramanujan, indeed displayed extraordinary mathematical talent from a very young age, earning him the label of a child prodigy. He was born on December 22, 1887, in Erode, a town in Tamil Nadu, India. Ramanujan’s mathematical abilities were evident early in his life, and he had an innate talent for discovering and formulating mathematical theorems.

Here are some notable aspects of Ramanujan’s early mathematical prowess:

  1. Self-Taught Genius: Ramanujan was largely self-taught in mathematics. His formal education in the subject was limited, and he had minimal exposure to advanced mathematical literature. Despite this, he independently developed numerous theorems and results.
  2. Mathematical Notations: Ramanujan often created his own unique notations and symbols to represent mathematical concepts. His notebooks were filled with formulas and theorems that he had derived on his own.
  3. College Years: Ramanujan entered the Government Arts College in Kumbakonam but faced challenges in completing formal education due to financial difficulties and his focus on independent mathematical exploration. His lack of interest in subjects other than mathematics affected his academic progress.
  4. Letter to G.H. Hardy: One of the turning points in Ramanujan’s life was when he wrote a letter to the British mathematician G.H. Hardy in 1913. In this letter, Ramanujan included a list of mathematical results he had discovered, many of which were new and profound. Recognizing the brilliance of Ramanujan’s work, Hardy invited him to England.
  5. Collaboration with G.H. Hardy: Ramanujan’s collaboration with G.H. Hardy at Cambridge University led to numerous groundbreaking contributions to mathematics. Hardy later described Ramanujan as one of the most original mathematicians of his time.

Despite facing challenges and health issues, Ramanujan’s contributions to mathematics had a lasting impact. Mathematicians all over the world continue to study and admire his work in number theory, modular forms, and other areas. Ramanujan’s story remains an inspiring example of raw mathematical talent and intuition.

The Indian government officially observed Srinivasa Ramanujan’s birthday, December 22, 2012, as National Mathematics Day in 2012. National Mathematics Day has been observed annually ever since. Additionally, 2012 was designated and observed as the National Mathematics Year.

Is a Soccer ball just a ball?

Even though this question might seem simple, a soccer ball isn’t a “ball”, as many people think. 

As crazy as it may sound, “A soccer is a Polyhedron”.

Polyhedron

A polyhedron is a three-dimensional shape with flat faces, straight edges, and sharp corners (vertices). The term “polyhedron” derives from the Greek words poly, meaning “many,” and hedron, meaning “surface.” When many flat surfaces are joined together, a polyhedron is formed. The names of these shapes are based on their faces, which are typically polygons.

It’s a truncated, 32-sided icosahedron with both pentagonal and hexagonal surfaces. It has 60 vertices and is one of the least known and most widely used shapes in the entire world. This is the geometry of soccer.

It has 20 hexagons and 12 pentagons on it.

A short video summarises this:

Pi (⌅) Day!!!

Earnmath wishes you all a very happy International pi day!!!

Pi day!!!

Math titbits

For example:

If we consider the three consecutive numbers 7,8 and 9

82 = 64

7 X 9 = 63.

Five Postulates of Euclidean Geometry

The elements of geometry, an exquisite and influential geometry treatise written around 300 B.C by the Greek mathematician Euclid, explains Euclidean geometry.

The five postulates form the foundation of euclidean geometry.