40 x 1000 = 40000
40 times 1000 is 40000. Count the zeros: one in 40, three in 1000, four in the answer, sitting behind the 4. It is also 200 squared, which is unusual for a round product.
40 × 1,000 = 40,000
Adding 40 to itself 1,000 times gives the same answer.
The working
Handle the digits that are not zeros first: 4 x 1 = 4. Then count the zeros, one in 40 and three in 1000, and write four of them behind the 4. That gives 40000.
40000 is a square number
200 x 200 = 40000, so the square root of 40000 is 200 exactly, with no decimal. Most round answers on this site are not squares, which makes this one worth remembering. It also divides cleanly by 200, 400, 800, 1000 and 2000, giving 200, 100, 50, 40 and 20.
Where 40000 shows up
A 40-hour week over 50 working weeks is 2,000 hours a year, so 40,000 hours is twenty years of full-time work. The same calculation covers 40 boxes of a thousand, 40 reams at a thousand sheets, or a 40-unit order billed per thousand.
The mistake to watch for
40 x 100 = 4000 has one zero fewer. That factor of ten is the most common slip on this pair, because 40 and 4 read the same at a glance and 100 and 1000 do too. Two sizes down, 4 x 100 = 400 is the same digits again.
The same 40 against bigger multipliers
| Calculation | Answer |
|---|---|
| 40 x 100 | 4000 |
| 40 x 1000 | 40000 |
| 40 x 10000 | 400000 |
Its neighbours in the thousands are 30 x 1000 = 30000 and 50 x 1000 = 50000. Everything else is in multiplication answers.