A man can do a piece of work in 5 days, but with the help of his son, he can do it in 3 days. In what time can the son do it alone ?

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  1. 7 days
  2. 8 days
  3. 7 and 1/2 days
  4. 6 and 1/2 days

Answer (Detailed Solution Below)

Option 3 : 7 and 1/2 days
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Detailed Solution

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Formula Used:

1. Work done by man in 1 day: M = 1/5

2. Work done by man and son together in 1 day: M + S = 1/3

Calculation:

We have,

⇒ M + S = 1/3

Substitute M = 1/5 into the equation:

⇒ 1/5 + S = 1/3

⇒ S = 1/3 - 1/5

⇒ S = (5 - 3) / 15

⇒ S = 2/15

Time taken by the son to complete the work alone is the reciprocal of S:

⇒ Time taken by son = 1 / (2/15)

⇒ Time taken by son = 15 / 2

⇒ Time taken by son = 7.5 days

∴ The correct answer is option 3: 7 and 1/2 days.

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Last updated on Jul 3, 2025

-> Indian Navy Tradesman Mate 2025 Notification has been released for 207 vacancies.

->Interested candidates can apply between 5th July to 18th July 2025.

-> Applicants should be between 18 and 25 years of age and must have passed the 10th standard.

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