So much work to do!

Algebra Level 4

Kamal and Sandeep start doing a task, working alternatively for a day each. The tasks gets done in exactly 13 days when Kamal start the task on the first day. And it takes exactly 13 1 3 13 \dfrac13 days when Sandeep start the task on the first day. In how many days will the task be done, if both work together on the task?

If your answer is a b \dfrac ab , where a a and b b are coprime positive integers, find a + b a+b .


The answer is 38.

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1 solution

Abhay Tiwari
Apr 30, 2016

We don't have to care about the first 12 12 days as in them same work is done in both the cases.

Lets assume :

One day work of K a m a l Kamal = 1 K \frac{1}{K}

One day work of S a n d e e p Sandeep = 1 S \frac{1}{S}

First Case: K a m a l Kamal starts the work and the last one to finish is K a m a l Kamal only, work done by him = 1 K \frac{1}{K} .

Second Case: S a n d e e p Sandeep starts the work and the last one to finish is S a n d e e p Sandeep only, with leaving one-third of the work which K a m a l Kamal can do in a day, Total work done= 1 3 K + 1 S \frac{1}{3K}+\frac{1}{S} .

Both the work done are equal, Therefore:

1 K = 1 3 K + 1 S \frac{1}{K}=\frac{1}{3K}+\frac{1}{S}

we get: 1 K = 3 2 S \frac{1}{K}=\frac{3}{2S}

From here we get, that K a m a l Kamal alone can finish the work in 11 11 days, while S a n d e e p Sandeep alone can finish the work in 33 2 \frac{33}{2} days.

They will finish the work together in X X days 1 X = 1 K + 1 S = 1 11 + 2 33 = 5 33 \frac{1}{X}=\frac{1}{K}+\frac{1}{S}=\frac{1}{11}+\frac{2}{33}=\frac{5}{33}

So X = 33 5 = a b X=\frac{33}{5}=\frac{a}{b}

a + b = 38 a+b=\boxed{38}

I think u messed upbwith the question. You have asked how much time do they take together . Its obivous both work simultaneously and not in parts .

Pawan pal - 5 years, 1 month ago

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They are working alternately first and then together. We have to find the time taken for them to finish the work together.

Abhay Tiwari - 5 years, 1 month ago

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