Question 13
Exercise 5. Find the digits represented by $a$ and $b$ in $\overline{a7889b}$ so that it is divisible by 15.
**Editorial input convention:** List all valid ordered pairs (a,b) by increasing a. Use parentheses, commas inside pairs and semicolons between pairs, with no spaces anywhere. Format example, not the answer: (1,2);(3,4). Different letters need not be different digits.
**Editorial input convention:** List all valid ordered pairs (a,b) by increasing a. Use parentheses, commas inside pairs and semicolons between pairs, with no spaces anywhere. Format example, not the answer: (1,2);(3,4). Different letters need not be different digits.