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There are 250 people in a museum.
2/5 of the 250 people are girls
3/10 of the 250 people are boys
The rest of the 250 people are adults
Work out the number of adults in the museum.

Correct answer:

a =  75

Step-by-step explanation:

$$\begin{gathered} n=250 \\ g=\frac{2}{5}\cdot n=\frac{2}{5}\cdot 250=100 \\ b=\frac{3}{10}\cdot n=\frac{3}{10}\cdot 250=75 \\ a=n-g-b=250-100-75=75 \end{gathered}$$

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