Rowing adolescents

The rowing club has 90 members. Four times as many older adolescents are in the section as younger adolescents. On the other hand, 54 fewer younger adolescents are in the section than older adolescents. How many older and younger adolescents are there?

Final Answer:

a =  72
b =  18

Step-by-step explanation:

$$\begin{gathered} a+b=90 \\ a=4b \\ a=4\cdot b \\ a+b=90 \\ a-4b=0 \\ Row2-Row1\to Row2 \\ -5b=-90 \\ b=\frac{-90}{-5}=18 \\ a=90-b=90-18=72 \\ a=72 \\ b=18 \end{gathered}$$

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