Question 4: \(\text { Find the digits } a \text { and } b \text { such that } ab=4 \text { and } \overline{87 ab} \text { is divisible by } 9\)
\(\begin{aligned} &\text { Because } ab=4 \Rightarrow a=b+4\\ & \text { where } \overline{87 ab} \text { is divisible by } 9 \Rightarrow 15+a +b \text { divisible by } 9 \\ &\Rightarrow19+2 \mathrm{~b} \text { divisible by } 9 \Rightarrow \mathrm{b}=4 ; \mathrm{a}=8 \text {. } \end{aligned}\)
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