GMAT OG 13

[email protected] wrote:132. Joanna bought only $0.15 stamps and $0.29 stamps.
How many $0.15 stamps did she buy?

(1) She bought $4.40 worth of stamps.
(2) She bought an equal number of $0.15 stamps
and $0.29 stamps.

Can someone explain to me why is statement 2 insufficient? Cant it be written as 0.15(x) + .29(y) = 4.40
since, x=y so we replace y=x in the equation above. Please explain?

In statement 2, all we know is that Joanna bought an equal number of $0.15 stamps and $0.29 stamps.
We don't know that she spent $4.40 (that info is in statement 1)

Cheers,
Brent

Be very careful to evaluate each statement individually! You were using what we called "statement carryover" - you were using the information from statement 1 in evaluating statement 2. This is a very easy mistake to make, but it will really hurt your score! You have to "forget" what you knew from the previous statement. I find that it's helpful to actually hold your hand over the first statement so you can only see the second one.

Focus on trying to PROVE INSUFFICIENCY! With the second statement, here are some possible scenarios:

one of each stamp: $0.15 + $0.29
100 of each: $15 + $29
10,000 of each: $1500 + $2900

As we can see, there's no way to tell how many $0.15 stamps we have.