Question 419350
Add their rates of typing
{{{1/40}}} is Jonathan's rate ( 1 document/40 min)
{{{1/30}}} is Susan's rate (1 document/30 min)
{{{1/24}}} is Jack's rate (1 document/24 min)
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Let {{{t}}} = the time in minutes with all 3 working together
{{{1/40 + 1/30 + 1/24 = 1/t}}}
Multiply both sides by {{{2}}}
{{{ 1/20 + 1/15 + 1/12 = 2/t }}}
Multiply both sides by {{{60t}}}
{{{3t + 4t + 5t = 120}}}
{{{ 12t = 120 }}}
{{{ t = 10 }}}
It will take them 10 min working together