Question

'a' and 'b' together can complete a
piece of work in 9 days. 'a' alone
can complete the work in 36 days.
The number of days 'b' alone take to
complete the work:
a) 18
b)30
c)12
d)14​

Answer 1

Answer:

c) 12

Step-by-step explanation:

Assume total work = 1

Let the total days took by a to complete work = A

Let the total days took by b to complete work = B

Work done by a in 1 day = $\frac{1}{\text{A}}$

Work done by b in 1 day = $\frac{1}{\text{B}}$

Work done by a and b in one day = $\frac{1}{\text{9}}$ =  $\frac{1}{\text{A}}$+ $\frac{1}{\text{B}}$

Work done by a and b in one day = $\frac{1}{\text{36}}$ = $\frac{1}{\text{A}}$

$\frac{1}{\text{9}}$ =  $\frac{1}{\text{36}}$ + $\frac{1}{\text{B}}$

$\frac{1}{\text{B}}$ =  $\frac{1}{\text{9}}$ - $\frac{1}{\text{36}}$

$\frac{1}{\text{B}}$ =

$\frac{1}{9}-\frac{1}{36}\\\\\frac{4 - 1}{36}\\\\\frac{1}{12}$

B = 12