There 14

There are 250 people in the 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:

$$\begin{gathered} n=250 \\ g=\frac{2}{5}\cdot n=\frac{2}{5}\cdot 250=\frac{2\cdot 250}{5}=\frac{500}{5}=100 \\ b=\frac{3}{10}\cdot n=\frac{3}{10}\cdot 250=\frac{3\cdot 250}{10}=\frac{750}{10}=75 \\ a=n-g-b=250-100-75=75 \end{gathered}$$

Try another example