vcbabu wrote:

. Both a, b, and c are 3-digits integers, where a=b+c. Is the hundreds' digit of number a equal to sum of that of b and c?

1). Tens' digit of a=tens' digit of b+tens' digit of c

2). Units' digit of a=units' digit of b + units' digit of c

This is basically a problem that asks us to determine whether there were any numbers carried over from the previous units in the addition process.

1 - Not enough. We know if the tens' digits do not add up to 10, then nothing will be carried over. We know the tens' digits of B & C do not add to 10, but we don't know whether anything carried over from the addition of the units' digits, which might in turn push the sum of the tens' digits over 10.

2 - Also not enough for the same reason above. We know the addition of the units' digits won't carry over to the tens, but we don't know anything about the tens' digits.

Combined: Enough, we know neither the units nor the tens will carry over additional numbers, so the sum of the hundreds' digits will not include anything carried over.