EgmatQuantExpert wrote:
A and B are two laborers who have been given the task to build a house. A can build a house in 20 days while B can build it in 30 days. But B went rogue and instead of building the house, he starts breaking it at the same rate. If A starts the work on the 1st day and they work alternately, in how many days will the house get built? (Assume once the house gets build, they will stop working)
A. \(60\) days
B. \(115\) days
C. \(120\) days
D. \(140\) days
E. \(121\frac{1}{3}\) days
To read all our articles:Must Read articles to reach Q51To solve question of the week:Question of the WeekA does 1/20th work in a day and B demolishes 1/30th the next day. So over 2 days, they together do
1/20 - 1/30 = 1/60th of the work.
This means, if they had continued like this, they would have needed 120 days to complete the work.
Day after day, they would have worked in this fashion: 1/20, -1/30, 1/20, -1/30 .... 1/20, -1/30, 1/20, -1/30 1/20, -1/30
But, we are given that the moment the work is done, the demolisher backs off. This means that the 1/60, 1/60, 1/60 work done in the last 6 days does not happen. On 115th day, A does 1/20th work and completes it. Then there is no 116th day on which the demolisher works.
Answer (B)