100 x 300 = 30000
100 times 300 is 30,000. Strip the zeros first: 1 x 3 is 3. Then put back all four zeros, two from the 100 and two from the 300, and you have 30,000.
100 × 300 = 30,000
Adding 100 to itself 300 times gives the same answer.
Count the zeros, not the digits
Both numbers are one small digit with zeros attached. Take the zeros off, multiply what is left, then put every zero back.
- 1 x 3 = 3
- 100 carries two zeros and 300 carries two zeros, so four in total
- A 3 followed by four zeros is 30,000
The dropped zero
The only real risk here is losing one. Three zeros gives 3000, and 3000 is the answer to 30 x 100, not to this. The gap between them is a factor of ten, which is the difference between a correct invoice and a badly wrong one. Count the zeros in both factors before you write anything down.
Other pairs that make 30,000
Zeros can be moved from one factor to the other without touching the product, so several pairs land on the same total. Pick whichever is easiest to hold in your head.
- 300 x 100
- 30 x 1000
- 3 x 10,000
How big 30,000 is
30,000 seconds is 8 hours and 20 minutes, so most of a working day. It is also 300 items at 100 each, and 30 lots of a thousand.
Next along: 100 x 1000 = 100000.