Problem
NT-B1-M12-P005 Set 1. Unknown Digit
#5
★☆☆☆☆ Level 1 of 5
Find the digit \(x\) if \(72x5\) is divisible by \(9\).
The digit sum must be divisible by \(9\).
The digit sum is \(7+2+x+5=14+x\). We need \(14+x\equiv0\pmod9\). Since \(x\) is a digit, \(x=4\).
Short check of a divisibility rule.