Carcass wrote:
OE
This question asks about television movies, which is divided into three subcategories. Vocational students spend 3% + 11% + 13% = 27% of their time watching these three types of TV movies. The question asks for a number of hours, though, so multiply this percentage by the final column to get a value. Vocational students spend 12.8 hours on average watching all kinds of prime-time television. Since you need an approximate answer, don't waste time doing specific calculations: 27% can be rounded to 25%, or one-fourth, and while normally 12.8 would be rounded up to 13, round it down to 12 as an easier fit with the percentage. Then 25% of 12 is 3, but be careful here; (D) is not the correct answer. The value 3 is what you get when you round both the percent and the total number of hours down, so the right answer has to be greater than 3. (E) is correct.
TAKEAWAY: Rounding is a great tool to help avoid potentially time-consuming calculations, but make sure you pay attention to whether you're rounding down or up. If you round values down and multiply or add them, the actual answer is going to be bigger than your estimate.
Analyze the table
The title "Average Weekly Viewing of Prime-Time Television" indicates that the chart deals with prime time only, and the chart breaks this viewing down further across genre categories, listed along the top of the chart, and viewer groups, listed down the left. Notice that these numbers are given as percents. The exception is the column on the far right, which shows the average weekly prime-time viewing in hours by viewer group. Nowhere are the numbers of each type of viewer given, so it is not possible to calculate the total number of hours of any genre watched by, say, preschoolers. To find the number of hours spent watching a prime-time program type for a particular viewer type, you'd need to multiply the percent at the intersection of that program/viewer type by the number of hours in the far right column for that viewer category.
Cool explanation and good point!
Approximation is a helpful tool for solving GRE problems, but like all tools, we must be careful about how we use them.