Two taps a and b can together fill a swimming pool in 15 days. the taps a and b are kept open for 12 days and then the tap b is closed .it took another 8 days for tap a to fill the pool. how many days does each tap require to fill the pool-navaneet 21 sets

Taps "a" and "b" fill the pool in 15 days.
In 12 days they fill 80% of the pool.
Working alone, it takes 8 days for tap "a" to fill 20% of the pool.
Therefore, working alone, it would take 40 days for tap "a" to fill the entire pool.

Using the attached formula:
Pipe "b" time = (40 * 15) / (40 -15)
Pipe "b" time = 600 / 25
Pipe "b" time = 24 days
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Double Check:
Total Time = (Pipe "a" time * Pipe "b" time) / (Pipe "a" time + Pipe "b" time)
Total Time = (40 * 24) / (40 + 24)
Total Time = 960 / 64
Total Time = 15 days
Correct!!!

Source:
http://www.1728.org/work.htm