45 x 100 = 4500
45 x 100 = 4500. Two zeros go on the end and the 45 stays where it is. Because 45 is half of 90, this answer is exactly half of 90 x 100.
45 × 100 = 4,500
Adding 45 to itself 100 times gives the same answer.
Why the answer is 4,500
Multiplying by 100 adds two zeros, so 45 becomes 4,500. Nothing carries, because 45 is already written in full before the zeros are attached.
Half of 9,000
45 is half of 90, so 45 x 100 is half of 90 x 100 = 9,000. If you know one of the two, you have the other in a single halving step. Doubling in the other direction works the same way.
4,500 divides cleanly
Add the digits: 4 + 5 + 0 + 0 = 9. A digit sum of 9 means the whole number divides by 9, and 4,500 / 9 = 500. It also splits as 45 = 9 x 5, so 4,500 = 9 x 500. That makes it an easy figure to share out.
What 4,500 counts
A 45 minute lesson repeated 100 times is 4,500 minutes, which is 75 hours. At 45 an hour, 100 hours of work bills 4,500.