If it takes 3 men to complete a job in 5 days, how long will it take 2 men to complete the same job?

Question

How do I use proportional thinking to solve this problem?

Answer 1

3 men do it in 5 days

1 man does it in 3x5 = 15 days 3 men are 3 times as fast. One man is 1/3 as fast as 3.

2 men are twice as fast as 1 man 15/2 = 7 1/2 days

3 men are 3/2 as fast as 2 men. 7.5/3/2 = 2(7.5)/3 = 15/3 = 5 days

each man does 1/15 of the job in a day

in 7.5 days 2 men do 7.5(1/15 + 1/15) = 7.5(2/15) = 15/15) = the job

answer: 7 1/2 days for 2 men