Mark's rate:
( 1 office cleaned ) / ( 30 min ) = 1/30
Lynn's rate:
( 1 office cleaned ) / ( 40 min ) = 1/40
Let (a) = the time in minutes for them
to clean the office working together
[tex] \frac{1}{30} [/tex] + [tex] \frac{1}{40} [/tex] = [tex] \frac{1}{a}[/tex]
Multiply both sides by 120a
4a + 3a = 120
7a = 120
a = 17.143
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CHECK YOUR ANSWER:
[tex] \frac{1}{30} [/tex] + [tex] \frac{1}{40} [/tex] = [tex] \frac{1}{a}[/tex]
0.0333 + 0.25 = [tex] \frac{1}{17.143} [/tex]
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The RIGHT answer is
17.143 minutes.
