Bunuel wrote:
A patient is given exactly 750 milliliters of a mixture of two medications daily. Medication A contains 40% pain killer and medication B contains 20% pain killer. If the patient receives exactly 215 milliliters of pain killer daily, how many milliliters of medication B are in the mixture?
A. 150
B. 225
C. 325
D. 425
E. 550
Medication A: 40% pain killer
Medication B: 20% pain killer
We combine medications to get TOTAL of
750 ml that's approximately 29% pain killer (215/750 ≈ 29%)
Important, if we combine EQUAL AMOUNTS of medications A and B (i.e., 375 mls of each), the TOTAL mixture is 30%.
Since the ACTUAL mixture is 29% , we know that this mixture has
MORE of medication A (20%) than medication B (40%)However, since 29% is very close to 30%, we know that a BIT MORE than half the mixture is medication B.
Check the answer choices to see that D (425) is a bit more than half.
Answer: D
For more on this concept, please see our free video on weighted averages -
http://www.gmatprepnow.com/module/gmat- ... /video/805Cheers,
Brent
Really nice logic solution. However, I think there is type error. Please review the highlighted part. it should be Medicine B (20%) and A (40%)