Remaining 83116

Ondra was reading a book. On the first day, he read one-tenth. On the second day, he read half of the remainder; on the third day, he read 20% of the new remainder; and on the fourth day, he read the remaining 72 pages. Thus, the book had 72 pages.

Correct answer:

n =  200

Step-by-step explanation:

$$\begin{gathered} d=72 \\ c-0.20\cdot c=d \\ c-0.20\cdot c=72 \\ 0.8c=72 \\ c=\frac{72}{0.8}=90 \\ c=90 \\ b-b/2=c \\ b-b/2=90 \\ b=180 \\ b=\frac{180}{1}=180 \\ b=180 \\ a-a/10=b \\ a-a/10=180 \\ 9a=1800 \\ a=\frac{1800}{9}=200 \\ a=200 \\ n=a=200 \\ \text{ Verifying Solution: } \\ B=a-a/10=200-200/10=180 \\ C=B-B/2=180-180/2=90 \\ D=C-0.20\cdot C=90-0.20\cdot 90=72 \\ E=D-D=72-72=0 \end{gathered}$$

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