1) we cannot determine 10s digits sum with units digit information. because whether the sum of 10s digits is greater than 9 or not cannot be determined. hence insuff.sud21 wrote:Integers x and y have three digits and z is the sum of x and y. Is the tens digit of z equal to the sum of the tens digits of x and y?
1). Both x and y have units digits greater than 6
2). The sum of tens digit of x and y is 7
Can you explain a bit further when you are taking both statements.user123321 wrote:1) we cannot determine 10s digits sum with units digit information. because whether the sum of 10s digits is greater than 9 or not cannot be determined. hence insuff.sud21 wrote:Integers x and y have three digits and z is the sum of x and y. Is the tens digit of z equal to the sum of the tens digits of x and y?
1). Both x and y have units digits greater than 6
2). The sum of tens digit of x and y is 7
2) with just 10s digits sum we cannot determine because we dont know information about units digit. hence insuff.
using both,
sum of units digit is greater than 6 =>
say, if unit digit sum is 8 then tens digit sum will be 7..ok
say, if tens digit sum is 12 then tens digit sum will be 7+1 = 8...not ok
so still insuff.
user123321
user123321 wrote:1) we cannot determine 10s digits sum with units digit information. because whether the sum of 10s digits is greater than 9 or not cannot be determined. hence insuff.sud21 wrote:Integers x and y have three digits and z is the sum of x and y. Is the tens digit of z equal to the sum of the tens digits of x and y?
1). Both x and y have units digits greater than 6
2). The sum of tens digit of x and y is 7
2) with just 10s digits sum we cannot determine because we dont know information about units digit. hence insuff.
using both,
sum of units digit is greater than 6 =>
say, if unit digit sum is 8 then tens digit sum will be 7..ok
say, if tens digit sum is 12 then tens digit sum will be 7+1 = 8...not ok
so still insuff.
user123321
mikemcgarry wrote: Remember that the fundamental task on DS is not to answer the question, but rather to determine whether you have enough information to answer the question. If you can give the original question either a definite yes answer or a definite no answer, that's sufficient. Insufficient means no definitive answer is possible.
Statement #1: Both x and y have units digits greater than 6
If the units digits of x and of y are both more than 6, then their sum will be more than 12. Therefore, a digit from the one's place will carry into the tens place, and the tens digit of Z cannot possibly equal the tens digit of X plus the tens digit of Y. This determines that the answer to the question is: No. Thus, we have determined a definitive answer to the question, and that is sufficient.
...
Therefore, the answer is A.
Does that make sense? Please let me know if there are any questions.
This bucket gets more and more disturbing, the more you think about it. but the question starts from introducing integers x and y. The digits are rather a form of the number expression. It's clear that there are only ten digits 0-9 and no one says that we need to apply -ve digit definition here.mikemcgarry wrote:In response to pemdas, I will say: when the GMAT talks about "digits", the assumption is that they are always talking about positive digits.
Since this question is not involving any specific type of number property relationship(s), such as prime number(s) or remainder(s), for which we would be allowed to make *blanket assumption* of +ve numbers, we need to read whether integers x and y are +ve or -ve. A *default assumption* (not *blanket*sud21 wrote:Integers x and y have three digits and z is the sum of x and y. Is the tens digit of z equal to the sum of the tens digits of x and y?
1). Both x and y have units digits greater than 6
2). The sum of tens digit of x and y is 7
) would be to consider all integers, i.e. positive and negative ones. 
