Average height

There are twice as many girls in the class as there are boys. The average height of girls is 177 cm, boys 186 cm. What is the average height of students in this class?

Correct answer:

a =  180 cm

Step-by-step explanation:

$$\begin{gathered} d=2c \\ a={\displaystyle \frac{177\cdot d+186\cdot c}{d+c}} \\ a={\displaystyle \frac{177\cdot 2c+186\cdot c}{2c+c}} \\ a={\displaystyle \frac{177\cdot 2+186\cdot 1}{2+1}}=180\text{ cm} \end{gathered}$$

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