Question

42. A takes 5 days more than B to do a certain job and 9
days more than C; A and B together can do the job in
the same time as C. How many days A would take to
do it?
(a) 16 days
(b) 10 days
(c) 15 days
(d) 20 days​

Answer 1

Answer:

15 days

Explanation:

let total work =1

time taken by A=t

time taken by B=t–5

time taken by C=t–9

Given

$\frac{1}{t} + \frac{1}{t - 5} = \frac{1}{t - 9} \\ (2t - 5)(t - 9) =t (t - 5) \\ {t}^{2} - 18t + 45 = 0 \\ (t - 15)(t + 3) = 0 \\ t = 15$