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IR Explained: Q31: Internet Usage
August 20, 2012
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In any Graphics Interpretation question, take a moment to understand all the components of the graphic.
Here, a line graph and a bar graph are shown on the same grid. The line graph represents world population and corresponds with the labels on the right side of the grid. The bar graph represents internet users and corresponds with the labels on the left side.
Both graphs represent a time period between 2001 and 2010, inclusive, with one data point for each year.
31A asks for a percent increase, for internet users from 2002 to 2007. Remembering to use the left-hand labels, note that there were about 700 (million) users in 2002 and 1,400 in 2007. The number doubled.
When an amount doubles, that's a percent increase of 100%. In mathematical terms, percent increase is given by change divided by original: (1400-700)/700, times 100%, or 700/700 = 1, times 100%.
31B involves more steps. To calculate how much the number of users per 100 people increased over a time span, you need to know the approximate number of users per 100 people at the beginning and endpoints of that span.
In 2000, there were roughly 400 (million) users out of 6100 people. In 2010, the corresponding numbers were 2100 and 6900.
Use the on-screen calculator, but keep things simple by aggressively approximating. No need to keep track of numbers to the third decimal place. 400 of 6100, or 4 of 61, is roughly 1 in 15, or 7 per 100. 2100 of 6900, or 21 of 69, is a bit less than 1 in 3 (that would be 23 of 69), so call it 30 per 100.
The increase, then, is from 7 per 100 to 30 per 100, or approximately 23 per 100. The only answer anywhere close to this is 24, which is correct.
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About the author: Jeff Sackmann has written many GMAT preparation books, including the popular Total GMAT Math, Total GMAT Verbal, and GMAT 111. He has also created explanations for problems in The Official Guide, as well as 1,800 practice GMAT math questions.
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