Question

an irrigation pump can do a job 3 times faster than another. If the y work together it takes 9 hours to complete the job. How long would it take the larger pump by itself

Answer 1

takes time t for pump 1 the big one
takes time 3 t for pump 2

so
pump 1 does 1/t jobs/hr
pump 2 does 1/3t jobs/hr

(1/t + 1/3t) = 4/3t jobs/hr together
(4/3t jobs/hr)9hr = 1 job
12 hours = t

Answer 2

1/t + 1/(3t) = 1/9