Problem Solving

A farm used two harvesting machines, H and K, to harvest 100 acres of wheat. Harvesting machine H, working alone at its constant rate, harvested 40 acres of wheat in 8 hours. Then harvesting machine K was brought in, and harvesting machines H and K, working together at their respective constant rates, harvested the remaining acres of wheat in 5 hours. Harvesting machine K harvested how many acres of wheat per hour?

(A) 7
(B) 8
(C) 12
(D) 13
(E) 15

OA: A

NandishSS wrote:A farm used two harvesting machines, H and K, to harvest 100 acres of wheat. Harvesting machine H, working alone at its constant rate, harvested 40 acres of wheat in 8 hours. Then harvesting machine K was brought in, and harvesting machines H and K, working together at their respective constant rates, harvested the remaining acres of wheat in 5 hours. Harvesting machine K harvested how many acres of wheat per hour?

(A) 7
(B) 8
(C) 12
(D) 13
(E) 15

OA: A

Let's call K's rate 'k' and H's rate 'h.'
We know h = 40 acres/8 hours = 5 acres/hour.

If h does 40 acres on its own, then there are 60 acres left to do. If those 60 acres are completed by both machines in 5 hours, then the combined rate is 60 acres/5 hours = 12 acres hour.

Because rates are additive in work problems, we now know that k + h = 12 or k + 5 = 12, so k = 7. The answer is A

How to deal with this kind of problems? I just bogged down seeing this...

Any link to deal with Word Problems & Work rate problem

NandishSS wrote:How to deal with this kind of problems? I just bogged down seeing this...

Any link to deal with Word Problems & Work rate problem

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