Question

P can do a job in 15 days in how many days p and q complete job if q is twise as fast as p

Answer 1

time taken by p to do work = 15 days
time taken by q to do the work= 15/2 because q is twice faster than p= 7.5

Answer 2

$p \: \: does \: \: job \: \: in \: \: 15 \: days \\ since \: \: q \: \: is \: \: twice \: \: as \: \: fast \: \: as \: \: p \\ q \: \: does \: \: job \: \: in \: \: \frac{15}{2 } = 7.5 \: days \\ \\ so \: \: they \: \: together \: \: complete \: \: job \\ in \: \: \frac{15 \times 7.5}{15 + 7.5} = 56.25 \: days$