We have inverse proportion
Inverse proportion occurs when one value increases and the other decreases.
More workers on a job would reduce the time to complete the task. They are inversely proportional.
2w ----------------------- 7h
3w ----------------------- xh
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(+) (-) ⇒ 2\3 = x\7 ⇒ x = 2·7/3=14/3 =12/3+2/3 =
= 4h + (2·60/3) min = 4h +40min