The fast method
⚡
270 - 27 = 243.
How it works
Multiply by 10 and subtract the original number. 9n = (10 - 1)n = 10n - n.
Why it works
9n = (10 - 1)n = 10n - n.
Use it when
Works for any real number.
Watch out for
Subtract the original number, not 1.
Verified examples
Example 1
27 × 9
270 - 27 = 243.
243Example 2
48 × 9
480 - 48 = 432.
432Example 3
63 × 9
630 - 63 = 567.
567