HOW TO BE A MATH WHIZ
Numbers are nice and neat, so they make really cool patterns. If you know those patterns, you can do some pretty cool math tricks in your head. Some tricks let you add and multiply big numbers in your head. It’s easy to multiply a 2-digit number by 11, and to “square” numbers ending in 5 (to square a number means to multiply it by itself). Our friend and fan Talie B. shared with us a video on “vedic” math…it even shows how to multiply big numbers by other big numbers in your head. Let’s learn some of the coolest number tricks out there, so you can wow your family and friends!
Wee ones: What digits do you use to “spell” the number 11?
Little kids: To multiply a 2-digit number by 11, you add its two digits and stick the answer in between them. So for example, 32 times 11 is 352, because 3+2=5. So what is 43 x 11? Bonus: What’s 72 x 11?
Big kids: When you multiply a number by 5, that’s half as much as multiplying by 10. So just cut the number in half, and tack on a zero. Quick, what’s 16 x 5? Bonus: What’s 42 x 5?
The sky’s the limit: To take any 2-digit number ending in 5 and multiply it by itself, you take the first digit, multiply it by the digit 1 more than it, and then just tack 25 onto the end. 35 x 35 is 1225, because 3 x 4 (the number 1 more than 3) is 12, and then you tack on 25…1225. So what’s 55×55?
Answers:
Wee ones: A 1 and another 1.
Little kids: 473 (because 4 + 3 = 7). Bonus: 792 (because 7 + 2 = 9). (Note: If the digits add to 10 or more, you use the last digit of that answer, and add 1 to the hundreds column. So 84 x 11 puts 12 in the middle, so it becomes 924 instead of 824.)
Big kids: 80. Half of 16 is 8, then tack on a zero. Bonus: 210. 21 is half of 42, then tack on a zero.
The sky’s the limit: 3025. 5 times the number 1 more than 5 (which is 6) gives you 5 x 6 = 30. Then tack on a 25, to get 3025.
Wee ones: What digits do you use to “spell” the number 11?
Little kids: To multiply a 2-digit number by 11, you add its two digits and stick the answer in between them. So for example, 32 times 11 is 352, because 3+2=5. So what is 43 x 11? Bonus: What’s 72 x 11?
Big kids: When you multiply a number by 5, that’s half as much as multiplying by 10. So just cut the number in half, and tack on a zero. Quick, what’s 16 x 5? Bonus: What’s 42 x 5?
The sky’s the limit: To take any 2-digit number ending in 5 and multiply it by itself, you take the first digit, multiply it by the digit 1 more than it, and then just tack 25 onto the end. 35 x 35 is 1225, because 3 x 4 (the number 1 more than 3) is 12, and then you tack on 25…1225. So what’s 55×55?
Answers:
Wee ones: A 1 and another 1.
Little kids: 473 (because 4 + 3 = 7). Bonus: 792 (because 7 + 2 = 9). (Note: If the digits add to 10 or more, you use the last digit of that answer, and add 1 to the hundreds column. So 84 x 11 puts 12 in the middle, so it becomes 924 instead of 824.)
Big kids: 80. Half of 16 is 8, then tack on a zero. Bonus: 210. 21 is half of 42, then tack on a zero.
The sky’s the limit: 3025. 5 times the number 1 more than 5 (which is 6) gives you 5 x 6 = 30. Then tack on a 25, to get 3025.