problem:
5 caterpillars need 30 days to cut a canal.
How many caterpillars are needed to cut the canal within 50 days?
answer:
1. step: proportion
* 30 days – 5 caterpillars
: 50 days – x caterpillars
2. step: which proportion?
↑ more days ↓less caterpillars = inverse proportion
3. step: formula
x = 5 * 30
50
x = 3 caterpillars
4. step: answer
3 caterpillars are needed.