The parallelogram

The circumference of the parallelogram is 79.5 m, and its shorter side is half the longer side. What is the length of which side of the parallelogram?

Correct answer:

a =  13.25 m
b =  26.5 m

Step-by-step explanation:

$$\begin{gathered} o=79.5\text{m} \\ 2(a+b)=o \\ a=b/2 \\ 2(a+b)=79.5 \\ a=b/2 \\ 2\cdot (a+b)=79.5 \\ a=b/2 \\ 2a+2b=79.5 \\ 2a-b=0 \\ Row2-Row1\to Row2 \\ 2a+2b=79.5 \\ -3b=-79.5 \\ b=\frac{-79.5}{-3}=26.5 \\ a=\frac{79.5-2b}{2}=\frac{79.5-2\cdot 26.5}{2}=13.25 \\ a=\frac{53}{4}=13.25 \\ b=\frac{53}{2}=26.5 \end{gathered}$$

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