Why the trick works
99 is 100 - 1. So any number times 99 equals that number times 100, minus the number once. Example: 58 x 99 = 5800 - 58 = 5742.
Extend it to 999
999 is 1000 - 1, so multiply by 1000 and subtract the number. Example: 27 x 999 = 27000 - 27 = 26973.
The same idea works for 101
101 is 100 + 1, so multiply by 100 and add the number. Example: 46 x 101 = 4600 + 46 = 4646.
Practice problems
- 64 x 99
Show answerHide answer
6400 - 64 = 6336.
- 37 x 99
Show answerHide answer
3700 - 37 = 3663.
- 42 x 999
Show answerHide answer
42000 - 42 = 41958.
References
Get faster with timed practice
Number Sense Pro builds timed practice sets from UIL categories at the difficulty you choose, then shows what you missed so you know what to review.
Buy Once on the App Store