melguy wrote:A feed store sells two varieties of birdseed : Brand A, which is 40% millet and 60% sunflower and brand B which is 65% millet and 35% sunflower. If a customer purchases a mix of the two types of birdseed that is 50% millet, what percent of the mix is brand A?
It would be nice if this question came with some answer choices, because it's quite possible that we could just use a bit of number sense to answer the question in a few seconds.
Brand A is 40% millet
Brand B is 65% millet
We want a combined mixture with 50% millet.
If we were to combine EQUAL amounts of Brand A birdseed and Brand B birdseed, then the percentage of millet in the new mixture would be the AVERAGE of the two brands.
That is, the percentage of millet in the new mixture = (40% + 65%)/2 = (105%)/2 = 52.5%
In other words, if the new mixture were comprised of 50% Brand A and 50% Brand B, then that new mixture would 52.5% millet.
That's already pretty close to our desire percentage of 50%
To get that 52.5% millet DOWN to 50% millet, we a little need
less of the 65% mixture (Brand B) and little
more of the 40% mixture (Brand A).
So, the correct answer will have a little more than 50% of Brand A in the mixture. So, I'd look for an answer choice like 55% or 60%.
So, if the answer choices looked like this...
A) 25%
B) 45%
C) 50%
D) 60%
E) 75%
... I'd confidently choose D and move on.
However, if the answer choices looked like this...
A) 40%
B) 45%
C) 50%
D) 55%
E) 60%
... I'd probably have to go back and actually do the work (as the experts in this thread have already done)
Although I'd already know that the correct answer is either D or E, in which case I might just test those answer choices.
RELATED VIDEO
- Weighted Averages:
https://www.gmatprepnow.com/module/gmat ... /video/805
