Correct Answer: Option A
let both pipes will run for x minutes. So in x minutes they fill x[1/20 + 1/30] =5x/60 =x/12
Only Pipe 2 will run for Rest of the time which is (18-x) minutes
So, it fills (18-x)(1/30)
So,
x/12 + (18-x)/30 = 1
=> [5x+ 36-2x]/60 =1
=> 3x = 60 -36
=> 3x=24
=> x =8
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