Doing well on the GMAT is a function of accuracy and timing. With only 75 minutes to complete 37 math questions, you have approximately 2 minutes to complete each question. You need to find ways save time, and the “halving and doubling” math tip described in the video and examples below will help you do that.
Let’s take a look at an example in which halving and doubling can save you time:
18 x 6
Note that you can construct a new equation with the same product by halving one number and doubling the other number. Because many students are more comfortable with 12x multiplication rather than 18x multiplication, let’s halve 18 and double 6 to create the following equation:
18 x 6
= (18/2) x (6 x 2)
= 9 x 12
= 108
Let’s try another example:
16 x 5.5
You can create an equivalent equation by halving 16 and doubling 5.5 to get the following:
16 x 5.5
= (16/2) x (5.5 x 2)
= 8 x 11
= 88
Let’s try a more complicated problem:
2.25 x 36
In the example below we will apply the technique twice, effectively multiplying one number by 4 and the other by 1/4.
2.25 x 36
= 4.5 x 18
= 9 x 9
= 81
Today’s article was brought to you by Beat The GMAT and Magoosh. To try more practice questions with similar video explanations, check out Smart GMAT Practice, which launches on July 7, 2010.