Problem Solving

ardz24 wrote:Sam and David agreed to complete a work in 14 days. They also agreed to forfeit thrice the amount of wages corresponding to the unfinished if they failed to complete the work in 14 days. As they could not complete the work in 14 days, they lost 3/8th of the amount that they would have together received had they completed the work in time. If Sam alone can complete the work in 80 days,the time that David alone would take to complete the work is

A. 20 days
B. 24 days
C. 30 days
D. 35 days
E. 40 days

Since they lost 3/8 of the amount that they would have together received had they completed the job on time and they actually forfeited thrice the amount of wages corresponding to the unfinished, we can relate these two quantities as: ⅜ = 3x, and so x = ⅛, which means that they only had 1/8 of the job unfinished. In other words, they finished 7/8 of the job.

We can let n = the number of days David would take to complete the work alone. We are given that Sam would take 80 days to complete the work alone; thus, his rate would be 1/80, and David's rate would be 1/n. Since they both worked 14 days, and they finished 7/8 of the job, we can create the following equation:

14 x 1/80 + 14 x 1/n = 7/8

14/80 + 14/n = 7/8

Multiply the equation by 80n we have:

14n + 1120 = 70n

1120 = 56n

n = 1120/56 = 20

Answer: A