Find the greatest number that divides 237, 388 and 618, leaving remainders 5, 11 and 9 respectively.

Subtract each remainder: 237 - 5 = 232, 388 - 11 = 377 and 618 - 9 = 609. Now $232=2^3\times 29,377=13\times 29$ and $609=3\times 7\times$ 29, so the HCF is 29. Answering 151 uses the difference 388 - 237 without subtracting the remainders; $58=2\times 29$ and $87=3\times 29$ do not divide all three numbers.