does anyone know any multiplication math tricks so you can do big problems in your head?

Answer 1

Know the squares. If you are given a problem like 34*24 and recognize this is (29 + 5)(29 - 5) = 29^2 - 5^2 = 841 - 25 = 816

(and notice 29^2 is easy because 29^2 = (30 - 1)^2 = 30^2 - 2*30 + 1)

Factor a number, sometimes you might notice an easy way to do part of it. For instance, 29*155 = 29*31*5 = 899*5 (which you know from above) = 4495. (and the last multiplication by 5 is easy because to multiply by 5 you only need to divided by 2 and shift the decimal point)

Associate: for something like 48*53 this is 48*(52 + 1) = 48*52 + 48 = (by above) 2496 + 48 = 2544.

Regroup to get nice numbers: 55*28 = 55*2*14 = 110*14 = 1540.

But the best tip is to practice and get familiar with the numbers. Don't ever use a calculator!

Answer 2

The 9 Times Quickie

1. Hold your hands in front of you with your fingers spread out.
2. For 9 X 3 bend your third finger down. (9 X 4 would be the fourth finger etc.)
3. You have 2 fingers in front of the bent finger and 7 after the bent finger
4. Thus the answer must be 27
5. This technique works for the 9 times tables up to 10.

The 4 Times Quickie

1. If you know how to double a number, this one is easy.
2. Simply, double a number and then double it again!

The 11 Times Rule #1

1. Take any number to 10 and multiply it by 11.
2. Multiply 11 by 3 to get 33, multiply 11 by 4 to get 44. Each number to 10 is just duplicated.

The 11 Times Rule #2

1. Use this strategy for two digit numbers only.
2. Multiply 11 by 18. Jot down 1 and 8 with a space between it. 1 --8.
3. Add the 8 and the 1 and put that number in the middle: 198

Answer 3

The nine trick: Subtract on from the number being multiplied by nine, the put the number which, added to it, equals nine. That tells you that number times nine. (You can also count to the finger, of ten, being multiplied by nine, then use the number of fingers before that finger for the first digit and the number of afingers after it for the second digit.)
To multiply any two digit number by eleven, simply seperate the first snat the last digit, then add them together for the number in the middle, carrying a one if necessary. Add the number again to get the result times twelve.
Any number times five results in the number for 1/2 of itself followed by zero if even, and the first full number less than 1/2 of itself followed by five if odd.

Answer 4

Another quickie is if you're multiplying by a number that's near an easy number:

637 * 998

This equals 637 * 1000 - 637 * 2 = 637000 - 1274 = 635726

(I actually did do that in my head, and then verified with a calculator)

Answer 5

Square numbers near fifty are quite impressive

e.g.


50 squared =2500 the numbers above are based on this.
51 squared = 2601
52 squared = 2704
53 squared = 2809
54 squared = 2916
55 squared = 3025

Just add 100 to the hundreds for each 1 you go higher and square the units.

Answer 6

for 5x__

if it is an even number, cut it in half then add 0 on th end.

if it is an odd number, cut it in half(without the .5) and take the lesser half and add 5 on the end.