40 x 100 = 4000
40 times 100 is 4000. Multiply 4 by 1 to get 4, then hand back the three zeros that 40 and 100 brought with them. The answer is four thousand.
40 × 100 = 4,000
Adding 40 to itself 100 times gives the same answer.
The working for 40 x 100
40 x 100 = 4000. Take the zeros off both numbers and you are left with 4 x 1, which is 4. 40 held one zero and 100 held two, so three zeros go back on.
The same answer from a different pair
Because the zeros are all that really move here, 1000 x 4 also gives 4000. Shifting a zero from one side of a multiplication to the other leaves the product untouched. 4 x 1000, 40 x 100 and 400 x 10 are three routes to one number.
4000 hours
A full-time week of 40 hours repeated 100 times comes to 4000 hours. For scale, a work year of 40 hours across 52 weeks is 2080 hours, so 4000 hours is a little under two years of full-time work. That is usually the practical meaning when this total shows up in a timesheet or a project estimate.
Do not reach for the extra zero
40 x 1000 is 40000, not 4000. Both start from 4, and the only difference is how many zeros the second number contributes. More products are indexed on the multiplication answers page.