Question 167533
Jim works at a rate of 1/30 of job per minute
Sue works at a rate of 1/45 of job per minute
Tony works at a rate of 1/90 of job per minute

now the are doing the job together

{{{(1/30)t+(1/45)t+(1/90)t=1}}}   multiply equation by 90

{{{3t+2t+t=90}}}--->{{{6t=90}}} {{{highlight(t=15)}}}minutes for all of them to do the job