Andrew can mow the lawn in 30 minutes and Nicholas can mow the same section of lawn in 45 minutes. Working together, in how many minutes could they mow the lawn? I know the answer is 18 minutes but I don't know how the answer was solved. HELP ASAP, please!!!
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Let's call the area of the lawn section $A$. Then Andrew can mow $A/30$ per minute, while Nicholas is able to mow $A/45$ per minute. Together, they therefore would mow $$ \frac{A}{30} + \frac{A}{45} = A \frac{30 + 45}{30 \cdot 45} = \frac{A}{18}$$ per minute. This straightforwardly means that they can finish the whole section in 18 minutes.
janosch
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