Avoiding Calculations on GMAT Problem Solving
Last time, we talked about how to avoid annoying calculations on Data Sufficiency. Its not so surprising that you can do this on DS, since you dont really have to solve all the way on this question type.
But you can avoid annoying calculations on Problem Solving, too! Try this problem from the GMATPrep free exams to learn how.
*According to the directions on a can of frozen orange juice concentrate, 1 can of concentrate is to be mixed with 3 cans of water to make orange juice. How many 12-ounce cans of the concentrate are required to prepare 200 6-ounce servings of orange juice?(A) 25
(B) 34
(C) 50
(D) 67
(E) 100
Ready? Okay, first, lets understand whats going on.
Glance: PS. Story problem. The answers are numeric and arent super easy but they arent too ugly, either.
Read: Mix 1 can concentrate with 3 cans water. Okay. Each can is 12 ouncesthey kind of snuck that detail in there, but I want to separate that out because I may need to use that by itself.
Okay, how many cans of concentrate do I need get 200 6-ounce servings ... wow. There are a lot of moving parts. I want a picture.
Jot:
I left some space in the middle to do the work. But Im not ready to do the work yet! First, I need to think about how I want to approach this.
The 6-ounce and 12-ounce thing is annoying me. I want those to be the same. How can I make that happen?
If you have 200 6-ounce servings, then youd have 100 12-ounce servings. Does that make this any easier to solve?
Ooh, I have an idea. Each batch of juice consists of 4 cans of liquid total, or (4)(12) ounces of liquid. (Dont multiply that out yetdont do more math than you have to! Were still just thinking here.)
Total, Im trying to get to (100)(12). How do I do that? (Okay, now you can actually do math!)
One batch = (4)(12)
ALL batches = (100)(12)
How to get from 4 to 100? 4(25) = 100. I need 25 batches of juice to get (100)(12). Each batch contains 1 can of concentrate, so I need 25 cans of concentrate. (If theyd asked me how much water, Id need (3 cans)(25 batches) = 75 cans of water.) Done!
The correct answer is (A).
See how long I held off any calculations? It was really tempting to turn (4)(12) into 48. Confession: I did actually jump straight to that in my head! But then I stopped myself, because 48 is an annoying number, especially when I knew I next had to deal with that 100. There isnt an obvious relationship between 48 and 100, so I didnt want to go down that path.
Instead, I wrote down that (4)(12) and left it alone until I had to do some math and discovered that I just made my task a whole lot easier.
Key Takeaways for Avoiding Calculations on PS:
(1) Set up the calculations, but dont solve unless / until you have to. First, think about what youre doing and where youre trying to go.
(2) Let your twinges of annoyance work for you. Whenever I get an ugh twingenot even a huge one, just a little one!I immediately stop trying to do the math and just think for a moment. If I dont see the path yet, I just leave that math for a moment and see what the next step is (as I did above). I can always multiply 4 and 12 later, if I need to.
(3) When youre reviewing problems, ask yourself where you could have saved yourself time, mental energy, and aggravation. Be demanding whenever you see anything annoying: there should be a way to make your life easier! (And, if there isnt, then maybe that problem is to hard to bother doing!)
* GMATPrep questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.