Twelve men take 6 hours to finish a piece of work. After the 12 men have worked for 1 hour, the contractor decides to call in 8 more men. How many more hours would 20 men take to complete the remaining work?
Answers
The answer is 3 hours.
This is a simple inverse proportion question.
So, understand, if 12 men can finish work in 6 hours, they can do 1/6th of the work in 1 hour.
So, in 1 hour, work done by 12 men = 1/6.
Work remaining = 5/6.
12 men ----- 6 hrs
20 men ----- x
x = 12*6/20
x = 18/5 hrs
That means 20 men can finish 5/18 of work in 1 hour.
Thus time to be taken by the 20 men to finish work = 5/18 * y = 5/6
y = 3 hours.
The answer is 3 hours.
12 men takes 6 hours to finish a piece of work
⇒ 1 hour = 1/6 of the work
Find the amount of work left after 1 hour
Work left = 1 - 1/6 = 5/6
Find the number of men available after 8 more joined in :
Total number of men = 12 + 8 = 20
Find the number of hours needed for 20 men to finish the work:
12 men = 6 hours
1 man = 12 x 6 = 72 hours
20 men = 72 ÷ 20 = 3.6 hours
Find the amount of work 20 men can do in 1 hour:
20 men can complete the work in 3.6 hours
⇒ 1 hour = 1 ÷ 3.6 = 5/18 of the work
Find the number of days needed to complete the remaining work:
Number of days = 5/6 ÷ 5/18 = 3 days
Answer: The 20 men will need 3 more days to finish the work.