Is r + s + t an even number? (1) rs is an odd number (2) t is an even

Question

Is r + s + t an even number?

(1) rs is an odd number
(2) t is an even number

unraveled · Answer

Is r + s + t an even number?

Assumption is all three are integers, otherwise fractions give different results.

(1) rs is an odd number
Both are odd then.

But nothing about t

INSUFFICIENT.

(2) t is an even number 
Nothing about r and s

INSUFFICIENT.

Together 1 and 2

r is odd
s is odd
t is even
r + s + t is even.

SUFFICIENT.

Answer C.

slk00 · Answer

Can we pls get the official solution to this? Why is it E?

Posted from my mobile device

DanTheGMATMan · Answer

(1) When rs is odd, this means both r and s are odd, IF they are integers at all. They could also not be integers, in which case everything is out the door. Either way we don't know about T
 Not sufficient

(2) We don't know anything about r or s.
 Not sufficient

This is tricky, but even together they are not sufficient, because r and s don't have to be integers. For instance, 3 times 5/3 equals 3, which is odd, but then r + s isn't an integer at all in that case. Or, they could both be odd integers, in which case r + s + t is even. So these are not sufficient together.

E

mojizohan · Answer

1. rs odd => both odd 
2. t even => t could be an any even integer  BUT  it could be 0 too since that's an Even number too. 
Hence E

Takeaway: ALWAYS take 0 or negative numbers into account when the question doesn't mention the number is a positive integer.

Is r + s + t an even number? (1) rs is an odd number (2) t is an even

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GMAT Data Sufficiency (DS) Questions

Is r + s + t an even number? (1) rs is an odd number (2) t is an even

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