maihuna wrote:To complete a certain work, A alone would take 3 times as many days as B and C together; B alone would take 5 times as many days as A and C together and C requires 7 times as many days as A and B combined. The number of days each will require is in ratio A:B:C?

2 4 6
3 5 7
4 6 8
5 6 7
6 8 10

Find daily rates (hourly rates) always:

In one day A does 1/3 of the job and B and C do 100% work in one day

B does 1/5 of job and A and C do 100% of work in one day

C does 1/7 of the job and A and B do 100% of work in 1 day

But to do 1/3 of a job in one day, A has to complete the job in 3 days.
Same applies to B and C. Hence only B is correct answer.

Choose B.

dtweah wrote:

maihuna wrote:To complete a certain work, A alone would take 3 times as many days as B and C together; B alone would take 5 times as many days as A and C together and C requires 7 times as many days as A and B combined. The number of days each will require is in ratio A:B:C?

2 4 6
3 5 7
4 6 8
5 6 7
6 8 10

Find daily rates (hourly rates) always:

In one day A does 1/3 of the job and B and C do 100% work in one day

B does 1/5 of job and A and C do 100% of work in one day

C does 1/7 of the job and A and B do 100% of work in 1 day

But to do 1/3 of a job in one day, A has to complete the job in 3 days.
Same applies to B and C. Hence only B is correct answer.

Choose B.

the three options are in rato not in absolute terms so 3 5 7 means the ratio of A:B:C will be in 3:5;7.

Let A take a days to complete a job, B takes b days and C takes c days
A's 1 day work = 1/a. (B+C)'s 1 day work = 1/b + 1/c
Now we have 1/a = 1/3 [1/b + 1/c] => 3/a = 1/b + 1/c => 4/a = 1/a + 1/b + 1/c

1/b = 1/5 [1/a + 1/c] => 6/b = 1/a + 1/b + 1/c

1/c = 1/7 [1/a + 1/b] => 8/c = 1/a + 1/b + 1/c

This gives us the ratio of 4:6:8

IMO C