Question

5. A does 80% of a work in 20 days. He then calls in B and they together finish the remaining work in 3 days. How long B alone would take to do the whole work? O 23 O 27 040 O 371/2​

Answer 1

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$Whole \: work \: done \: by \: A\\ =20× \frac{5}{4} =25 \: days$

$Now$

$( 1 - \frac{4}{5} ) \: i.e$

1/5 is work done by A and B is three days

Whole work done by B and A in

$(3 \times 5) = 15 \: days$

A's 1 st day work

$= \frac{1}{25}$

A+ B 1st day work

$= \frac{1}{15}$

B' s 1 st day work

$= \frac{1}{15} - \frac{1}{25} = \frac{4}{150} = \frac{2}{75}$

So ,B alone would do the work in

$\frac{75}{2} = 37 \frac{1}{2} \: days$

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Answer 2

Answer:

Whole work done by A = 20 x 5/4 = 25 days

Now (1 - 4/5) i.e

1/5 is work done by and B is three days

Whole work done by B and A in (3 x 5) = 15 days

A's 1 st day work =1/25

A+B 1st day work = 1/15

B's 1st day work

= 1/15 - 1/25 = 4/150 = 2/75

So,B alone would do the work in

75/2=371/2 days