The largest 5-digit number is 99972. This is the largest divisible by 36, the product of 4 and 9 and was obtained by dividing 99999 (the largest 5-digit number) by 36 (or dividing 11111 by 4), taking the integer part of the quotient and then multiplying this integer by 36. 11111/4=2777+3/4. Integer part is 2777, multiplied by 36=99972.