Question 221213
Add the rates of producing cans for each machine
to get the rate for both machines working together
Let the time for both machines woking together
to make {{{7200}}} cans  = {{{x}}} min
given:
Rate of newer machine = {{{7200/200}}} cans/min
Rate of older machine = {{{7200/300}}} cans/min
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I can write the equation as
{{{7200/200 + 7200/300 = 7200/x}}}
Divide both sides by {{{7200}}}
{{{1/200 + 1/300 = 1/x}}}
Multiply both sides by {{{600x}}}
{{{3x + 2x = 600}}}
{{{5x = 600}}}
{{{x = 120}}}
Working together, it takes them 120 minutes to make 7200 cans