You might have noticed that some people seem to be able to do math like magic, or maybe you think these people are geniuses. Well, they might be, but more likely they have learned a few methods that make mental math a lot easier.
Follow these tips to speed up your multiplication and division talents!
The main thing to keep in mind when multiplying is to disregard (at first) any zeroes on the right side of whole numbers.
Multiplying
Example 1
1,400 x 60 is the same as 14 x 6 with three zeroes added back.
1,400 x 60 = 14 x 6 (+ 3 zeroes) = 84, 000
You are simply adding in the three zeroes to the right of the whole numbers that you disregarded earlier.
Easy!
Don’t forget to add your zeroes back in when multiplying.
Example 2
80 x 60 = 8 x 6 (+ 2 zeroes) = 4,800
Example 3
4,000 x 15, 000 = 4 x 15 (+ 6 zeroes) = 60, 000, 000
Dividing
When dividing, you can cancel an equal number of right hand zeroes.
Example 4
900 ÷ 30 = 90 ÷ 3 = 30
(Note that I can’t cancel the other zero in 900 because there was only one zero in 30. It has to be an equal number for division.)
Example 5
12,000 ÷ 200 = 120 ÷ 2 = 60 (I could cancel two zeroes on both sides.)
Note: In the two examples above notice that you can disregard the zero in 90 and 120 to divide and then add it back in! (12 ÷ 2 = 6 + one zero = 60)
Keep in mind that this method only works when zeroes comprise the entire right-hand portion of the number. It would not work, for example, with 900 ÷ 32.
Try a few questions yourself using these tips and then check with your calculator to make sure you are correct. (Mental math or pencil & paper only at first.)
You can do it!
- 30 x 7
- 14 x 500
- 600 x 30
- 70 x 120
- 4,900 ÷ 7
- 2,700 ÷ 90
- 24,000 ÷ 60
- 3,900 ÷ 130