Question 368877
Jill's rate: {{{1/30}}}
Sue's rate : {{{1/45}}}
Tony's rate: {{{1/90}}}
.
.
.
All together, their rate is {{{1/30+1/45+1/90}}}
Rate*Time=Output
Time=Output/Rate
{{{t=1/(1/30+1/45+1/90)}}}
{{{t=1/(3/90+2/90+1/90)}}}
{{{t=1/(6/90)}}}
{{{t=90/6}}}
{{{highlight(t=15)}}}minutes