<PRE><B>Question 875164</B>
A does 80% of a work in 20 days. He then calls in B and together they finish the remaining work in 3 days. How long B alone would take to do the whole work.
A completed 80% work in 20 days 
A can complete the full work in 25 days 
A 1 day work will be =1/25 parts 
task complete by A in 20 days =80/100 =4/5
remaining work  =1-4/5  =1/5 (1)
let b can complete full work in X days 
B 1 day work will be =1/X part
A and B 1 day work together will be = 1/25+1/x
                                    = X+25/25X
A and B  3 days work will be = 3(x+25)/25x (2)
by given conditions  equation 1 and 2 will be equal
1/5=3x +75/25x
25X = 5(3X +75)
25x= 15X + 375
25x-15x =375
10 X=375
X=37.5 days 
B alone can complete whole work in 37.5 days OR  75/2 days  Answer

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