Re: Successive Discount
There is no need to find the exact HCF in this case. You can directly check with the options easily. (Answer option + 8) must be the HCF of the three numbers. And it can be easily checked that 15 + 8 = 23 doesn't divide 231, 10 + 8 = 18 doesn't divide 189 and 21 + 8 = 29 also doesn't divide any of them.
So answer will be d.