Cookie division

Mom baked a bowl of cookies. The son took two-fifths of the cookies and the daughter one-quarter of the rest. What part was left to the parents?

Final Answer:

x =  9/20

Step-by-step explanation:

$$\begin{gathered} a=1-\frac{2}{5}=\frac{1\cdot 5}{5}-\frac{2}{5}=\frac{5}{5}-\frac{2}{5}=\frac{5-2}{5}=\frac{3}{5}=0.6 \\ b=\frac{1}{4}\cdot a=\frac{1}{4}\cdot \frac{3}{5}=\frac{1\cdot 3}{4\cdot 5}=\frac{3}{20}=0.15 \\ x=a-b=\frac{3}{5}-\frac{3}{20}=\frac{12}{20}-\frac{3}{20}=\frac{12-3}{20}=\frac{9}{20}=0.45 \end{gathered}$$

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