Times Table Answers

400 x 100 = 40000

400 times 100 is 40000. Both numbers are squares, which gives an unusually quick way to check the answer without redoing the multiplication. The working and that check are below.

400 × 100 = 40,000

Adding 400 to itself 100 times gives the same answer.

The working

Strip the zeros: 4 x 1 = 4. Put back the two zeros from 400 and the two from 100, four altogether, and the answer is 40000. Forty thousand.

Both factors are squares, so the answer is one too

400 is 20 x 20 and 100 is 10 x 10. Multiply two square numbers and the result is always a square, with a root equal to the product of the two roots: 20 x 10 = 200. So 40000 = 200 x 200. Squaring 200 is easy enough to do in your head, which makes it a genuine second opinion on the answer rather than the same sum repeated.

Another route to the same place: 100 x 100 = 10000, and 400 x 100 is simply four of those, 4 x 10000 = 40000.

One zero either way

Each line adds one zero. When an answer here looks nearly right, it is almost always a missing or extra zero rather than a bad multiplication, so count them before you check anything else.

The number 40000

40000 is a 4 followed by four zeros, written 40,000 with a separator. Its prime factors are only 2s and 5s, six of one and four of the other. More pairs on the multiplication answers page.