Bricklayers

Eight bricklayers build a house for 630 days. How many bricklayers must be added after 150 days to complete the building in (next) 320 days?

Correct answer:

n =  4

Step-by-step explanation:

$$\begin{gathered} a=8 \\ m=630\cdot a=630\cdot 8=5040 \\ a\cdot 150/m+(n+a)\cdot 320/m=1 \\ a\cdot 150+(n+a)\cdot 320=m \\ 8\cdot 150+(n+8)\cdot 320=5040 \\ 320n=1280 \\ n=\frac{1280}{320}=4 \\ n=4 \end{gathered}$$

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