PROBLEM:
When 391758 and 394915 are divided by a certain three digit number, the three digit reminder is the same in each case. Find the divisor.

Nick,

What can you say about the difference of the two given numbers? (If it is not obvious what this means, give yourself an easier problem to practice with: 394 and 317 are divided by a 1-digit number and the 1-digit remainder is the same in each case; find the divisor. So 394-317 = ?. What are the divisors of this difference? Which divisor is a single digit? These two numbers (394 and 317) must leave the same remainder after division by 7 since their difference is divisible by 7.)

Chris and Sue