Question 25: Find the digits x, y such that the number \(\overline {159xy} \) is divisible by both 5 and 9

Because \(\overline {159xy} \) 5 \(\left[\begin{array}{l}y=0\\y=5\end{array}\right\)

+ If y = 0, we have: \(\overline {159×0} \). This number is divisible by 9 when (1 + 5 + 9 + x) 9

x = 3

+ If y = 5, we have: \(\overline {159×5} \). This number is divisible by 9 when (1 + 5 + 9 + x + 5) 9

x = 7

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