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DS prob, how to go about this quickly?

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by arpan307 » Fri May 20, 2011 10:45 pm
I need a quicker way of solving such problems...

Q. 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.

Its an OG 12 problem. I chose E but the OA is A. How to quickly check the equation formed by (1)?
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Source: — Data Sufficiency |
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by Frankenstein » Sat May 21, 2011 1:16 am
Hi,
Lets say he bought 'a' number of 0.15$ stamps and 'b' number of 0.29$ stamps.
From(1) (0.15)a+(0.29)b = 4.40 => 15a + 29b = 440 =>15a = 440-29b
So, RHS(Right Hand Side) should have either 5 or 0 as the units digit for this to hold. so, b belongs to {0,5,10,15}
If we try the values, only b=10 satisfies which gives a=10. Hence, (1) is sufficient.

(2) is insufficient

Cheers!
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