 # 10 Cool Math Facts and Tricks The word “dyscalculia” sounds fancy but it really just serves as a broad term for learning difficulties in math. The good news is that dyscalculia is often due to poor visual processing and memory skills, which means we can address the root cause of math struggles by strengthening those skills with cognitive skills training (a.k.a. “personal brain training”). Once those cognitive skills are strong, you can use some of the following cool math facts and tricks to excel in your new favorite subject! Here are some cool math facts and tricks to get you started.

1. If you multiply any number by nine then add all the digits of the product until you get a single digit, it will always be nine! For example:

9 x 123 = 1,107

1 + 1 + 0 + 7 = 9

1. The opposite sides of a die always total seven.
1. According to the “Birthday Paradox,” in a room of 23 people, there’s a 50-50 chances that two people will share a birthday. In a room with 75 people, there’s a 99.9% chance.
1. All numbers are divisible by three if the sum of its digits is divisible by three. For example:

Can you divide 12,345 by 3?

1 + 2 + 3 + 4 + 5 = 15

Since 15 is divisible by 3, the answer is “Yes, 12,345 is divisible by 3.”

1. Among all shapes with the same perimeter, a circle has the largest area.
1. The numbers 2 and 5 are the only primes that end in 2 or 5.
1. When multiplying a whole number by a power of 10, just count the zeros and add them to the right of your whole number. For example:

123 x 100,000

There are five zeros so the answer is 12,300,000.

1. To find 75 percent of a number, just multiply it by three then divide the product by four. For example, to get 75% of 500:

500 x 3 = 1,500

1500 divided by 4 = 375

1. If you have large numbers to multiply, as long as at least one of the numbers is even, you can subdivide until it’s simpler. (Start dividing the even number by two, while multiplying the other side by two.) For example:

120 x 125 = ? is the same as:

60 x 250 = ? is the same as:

30 x 500 = ? is the same as:

15 x 1000 = 15,000

10. The “Golden Ratio” is a special number that is approximately equal to 1.618. It has been used by artists and architects for centuries to create what is believed to be the most pleasing proportions in design.