# Five pupils

Five pupils clean 30 chairs one hour before four pupils. How many chairs clean one pupil in 1 hour?

Correct result:

n =  1.5

#### Solution:

$5n(t-1)=30 \ \\ 4nt=30 \ \\ \ \\ 5nt - 5n=30 \ \\ 4nt=30 \ \\ \ \\ \ \\ 5 \cdot \ 30/4 - 5n=30 \ \\ \ \\ 5 \cdot \ 30/4 - 5 \cdot \ n=30 \ \\ \ \\ 20n=30 \ \\ \ \\ n=\dfrac{ 3 }{ 2 }=1.5t=30/(4 \cdot \ n)=30/(4 \cdot \ 1.5)=5=\dfrac{ 3 }{ 2 }=1.5$

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