Question

Mark (✓) against the correct answer
70% of students in a school are boys. If the number of girls is 240, how many boys are there in the school?

(a) 420
(b) 560
(c) 630
(d) 480

Answer 1

(b) 560

Let the total number of students be 100.
Then, number of boys = 70
∴ Number of girls = (100 − 70) = 30

Now, total number of students if there are 30 girls = 100
Total number of students if there are 240 girls = $\left(\frac{100}{30}\times 240\right)=800$
∴ Number of boys = (800 − 240) = 560

Hence, there are 560 boys in the school.