Procrastinating the Right Way
Joe’s Pizzeria hands out 25% off coupons to its customers. If each pizza costs Joe $6 to make and he needs a 25% profit on each pizza’s sales, what price should Joe charge per pizza?
Most people would look at this question and attack it by first adding 25% to 6. However, you would then have to multiply by the inverse of 75% (or 1.33) to solve the remainder of the question. This approach is a perfectly viable option. However, this method also forces you to work with more complex numbers than you may be comfortable dealing with in your head, opening up possibilities for all sorts of mathematical errors.
By using the deferred calculations method, you avoid these potential pitfalls. Here is how it works. We know that the customers only pay 3/4 the cost of the final sale price due to the 25% off coupon. We also know that netting a 25% profit on the cost is equal to 5/4 of the cost. Written algebraically, this leaves us with 3/4 price = 5/4 cost. From here we simply have to plug in the values and solve. First, move 3/4 to the other side of the equal sign by multiplying by its reciprocal to get price = 5/4 cost x 4/3. Next, cancel out both of the 4s to get price = 5 cost x 1/3. Now plug in 6 for the cost and divide it by 3 to get 2. This leaves us with price = 5 x 2 which is 10.
Using this method has several benefits. Firstly it cuts back on the amount of mental math you will have to perform. While mental math is an essential skill to learn for the quantitative section, any time you can lessen the number of calculations you need to do in your head will reduce the number of opportunities you have to make an error. Additionally, doing all your math at the end of the problem, and at the same time, allows you to trace back any mistakes more quickly than if your calculations were spread out across the entire process of solving the question. In the end, the correct answer can be reached by using either method, but in instances such as the example above, the deferred calculations method allows you to solve the question faster and with less chance for errors.
There will be multiple ways to approach many of the questions that you encounter on the GMAT. While any number of them could lead you to the correct answer, success on the GMAT depends not only upon how accurate you are, but also on how efficiently you can answer questions.