Question

Computer a can carry out an engineering analysis in 6 hours, but computer b can do the same job in 4 hours. how long does it take to complete the job if both computers work together?

Answer 1

Computer A can carry out analysis in 6 hours. That means in an hour, computer A does $\frac{1}{6}$ of the job.

Computer B can carry out analysis in 4 hours. That means in an hour, computer B does $\frac{1}{4}$ of the job.

If both computers work together, in an hour they do:
$\dfrac{1}{6}+ \dfrac{1}{4}$
$= \dfrac{2}{12}+ \dfrac{3}{12} \text{(equalize the denominators)}$
$= \dfrac{5}{12}$
In an hour, they do $\frac{5}{12}$ of the job.

To finish the job, they need $\frac{12}{5}$ hours.
$\dfrac{12}{5}$ hours
= 2.4 hours
= 2 hours + 0.4 hour
= 2 hours + 0.4 × 60 minutes
= 2 hours 24 minutes

They finish analysing in 2 hours 24 minutes