Question

Multiple Choice Questions (MCQs)
15. A and B together take 5 days to do a work, B
and C take 7 days to do the same and A and C
take 4 days to do it. Who among these will take
the least time, if put to do it alone?
(a) A
(b) B
(c)
(d) data is not adequate​

Answer 1

Step-by-step explanation:

A

bcoz A when work with B take less time and when works with C took more less time

Option A 100% sure

Answer 2

Answer:

Hola...

Step-by-step explanation:

A and B together take 5 days to do work. B and C take 7 days to do the same work, and A and C take 4 days to do it. Who among these will take the last time if put to do it alone?

A and B together do 1/5th of the work in a day.

B and C together do 1/7th of the work in a day.

A and C together do 1/4th of the work in a day.

Add the three fractions.

2A, 2B and 2C together do (1/5) + (1/7) + (1/4) = (28+20+35)/140 = 83/140, so

A, B and C together do 83/(2*140) = 83/280th part of the work in a day. And all three working together will complete the work in 280/83 = 3.373493976 days. Now to find out who is the most efficient.

C working alone will do (83/280)-(1/5) = (83–56)/280 = 27/280 = 1/10.37037037th part of the work in a day.

B working alone will do (83/280)-(1/4) = (83–70)/280 = 13/280 = 1/21.53846154th part of the work in a day.

A working alone will do (83/280)-(1/7) = (83–40)/280 = 43/280 = 1/6.511627907th part of the work in a day.

So A is the most efficient and he will do the job in 6.511627907 days.

Next comes C who will do the job in 10.37037037 days.

And the least efficient is B who will do the job in 21.53846154 days.

So, your answer is (a) A

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