0.003 x 10000 = 30
0.003 times 10000 is 30. Multiplying by 10000 moves the decimal point four places to the right, so 0.003 becomes 30. That is the same as taking 0.3 percent of 10000.
0.003 × 10,000 = 30
The working
0.003 is three thousandths, or 3/1000. Dividing 10000 by 1000 leaves 10, and three of those is 30. Shifting the decimal point gives the same answer in one motion, four places at a time:
0.003 to 0.03 to 0.3 to 3 to 30.
Count the places against the zeros in 10000. Four zeros, four places. That check is worth doing every time, because this is a pair where being one place out is easy and invisible.
Reading 0.003 as a rate
Small decimals like this one are usually a rate rather than a quantity. As a percentage, 0.003 is 0.3%. In basis points, where one point is 0.0001, it is 30 basis points. So a 30 basis point charge applied to 10,000 comes to 30 units, which is why this exact calculation shows up in fee and interest work rather than in schoolwork.
The two near misses
- 0.003 x 1000 = 3, one place short of this answer.
- 0.03 x 10000 = 300, one place long.
Both are wrong by a factor of ten, and both look plausible written down.
Related calculations
Other small decimals worked the same way: 0.07 x 1000 = 70 and 0.006 x 100 = 0.6. For the whole-number version, see 10000 x 10 = 100000.