Question

The Lyndhurst High School twelfth graders are represented in the circle graph in Figure 1. Figure 2 is another way to illustrate the use of computers by these twelfth graders. If the same $200$ twelfth graders are represented in both figures, what is the total number of twelfth graders represented by the shaded circle in Figure 2?

Answer 1

Shaded region in figure $2$ represents students who uses computers at school which is equal to the sum of students who use computers only at school and the students who use computers at both school and home.

$70$ percent use computers at both home and school
$20$ percent use computers only at school
Therefore $70+20=90$ percent students use computers at school/
$\frac{90}{100}\times 200=180$( there are totally $200$ students)
Therefore, there are $180$ students who use computers at school( it represents shaded region in figure $2$).