0.07 x 1000 = 70

Move the point three places

Multiplying by 1000 moves the decimal point three places right, one place for each zero. Walk 0.07 across and you pass 0.7, then 7, then land on 70. As a fraction it is just as clean: 0.07 is 7 hundredths, and 7 hundredths of 1000 is 7000 divided by 100, which is 70.

This is really 7 percent

0.07 is how 7 percent is written as a decimal, so nearly everyone doing this sum is working out 7 percent of 1000: a sales tax line, an interest rate, a commission, a service charge. The answer is 70 either way. If the rate moves, use the fact that 1 percent of 1000 is 10, so multiply the percentage by 10 and stop.

The two wrong answers

The usual slips are 700 and 7. You get 700 by moving the point four places instead of three, and 7 by moving it two, which is a different calculation entirely. Count the zeros in 1000 before you start, then move exactly that many places.

Other decimals handled the same way: 1.4 x 1000 = 1400, 0.1 x 100 = 10 and 0.006 x 100 = 0.6. The rest are indexed on multiplication answers.