A man and his son planned to paint their own house. The man alone can do in 20 days. He paints for 4 days and then his son completed in 8 days. Find how many days will they take working together?
a) 12 days b) 11 days c) 7 days d) 8 days
Man takes 20days alone so for 4 days, he will do 1/5 work. Left work will be 4/5 which the son does in 8 days, so, alone, boy takes 10 days and together, they will take 1/10 + 1/20 days, that is 7 days.
Answer is option (c) 7 days Explanation: Man's 1 day work = 1/20 Then 4 days work = 4/20 = 1/5 Remaining work = 1 - 1/5 = 4/5 Now, 4/5 work is done by the son in 8 days. Then, whole work will be done by him in (8 x 5/4) days = 10 days. Then his 1 day work = 1/10 The man and his son's 1 day work = 1/10 + 1/10 = 3/10 They will complete the work together in 20/3 days = 6 2/3 days = 7 days(nearly). Hence the answer is 7 days.