A and B each working alone can do a work in 15 days and 25 days, respectively. They started the work together but B left after some time and A finished the remaining work in 7 days. After how many days from the start did B leave?
Correct Answer: 5
Explanation:
Let B left work after N days from the start.
According to the question,
N/25 + (N + 7)/15 = 1
⇒ (3N + 5N + 35) / 75 = 1
⇒ 8N = 75 - 35
⇒ N = 40/8
∴ N = 5
