57. A takes 6 days less than B to do a work. If both A and B working together can do it in 4 days, how
many days will B take to finish it?
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Step-by-step explanation:
given
A+B together finish work in 4 days
A takes 6days less than B
let B finish x days and A finish x-6 days
a/c to question
=>1/x-6+1/x=1/4
=>x+x-6/x(x-6)=1/4
=>2x-6/x^2-6x=1/4
=>x^2-6x=8x-24
=>x^2-6x-8x+24=0
=>x^2-14x+24=0
=>x^2-12x-2x+24=0
=>x(x-12)-2(x-12)=0
=>(x-12)(x-2)=0
=>x-12=0,x-2=0
=>x=12,x=2
x=2is not correct because A cannot negative
so B finish work in 12 days.
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