The sum of positive integers x and y is 77. What is the value of xy?
1). x=y+1
2). x and y have the same tens' digit.
I am not sure what level 600 + / 700 + these level of questions are .....
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
Number Systems
This topic has expert replies
GMAT/MBA Expert
-
[email protected]
- Elite Legendary Member
- Posts: 10392
- Joined: Sun Jun 23, 2013 6:38 pm
- Location: Palo Alto, CA
- Thanked: 2867 times
- Followed by:511 members
- GMAT Score:800
Hi sukhman,
For this DS question, you can use a combination of algebra rules and TESTing values:
We're told that X and Y are positive integers and X + Y = 77. We're asked for the value of (X)(Y).
Fact 1: X = Y + 1
We don't actually have to do any work here. Combined with the information in the prompt, we have a 2-variable "system" (2 variables, 2 unique equations), which means you CAN solve and get the values of X and Y. In this case, it's 39 and 38, which would allow you to solve (38)(39).
Fact 1 is SUFFICIENT
Fact 2: X and Y have the same "ten's digit"
Since the sum is 77, then the "ten's digit" for both has to be a 3.
While this might not seem like enough information, you should attempt to "play around" and see if there are multiple options or just one.
Obviously 38 and 39 fit.
One of the numbers CAN'T be 37, because the other would then be 40 (and the ten's digit is supposed to start with a 3). No other possibility exists, so there's just the 38 and 39.
Fact 2 is SUFFICIENT
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
For this DS question, you can use a combination of algebra rules and TESTing values:
We're told that X and Y are positive integers and X + Y = 77. We're asked for the value of (X)(Y).
Fact 1: X = Y + 1
We don't actually have to do any work here. Combined with the information in the prompt, we have a 2-variable "system" (2 variables, 2 unique equations), which means you CAN solve and get the values of X and Y. In this case, it's 39 and 38, which would allow you to solve (38)(39).
Fact 1 is SUFFICIENT
Fact 2: X and Y have the same "ten's digit"
Since the sum is 77, then the "ten's digit" for both has to be a 3.
While this might not seem like enough information, you should attempt to "play around" and see if there are multiple options or just one.
Obviously 38 and 39 fit.
One of the numbers CAN'T be 37, because the other would then be 40 (and the ten's digit is supposed to start with a 3). No other possibility exists, so there's just the 38 and 39.
Fact 2 is SUFFICIENT
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
