In a school, the ratio of boys to girls is 7:5. If 30 more girls join, the ratio becomes 7:6. Find the number of boys.
Show answer & explanation
Correct answer: A
Explanation
Given:
Boys : Girls = 7 : 5
New ratio when 30 girls are added = 7 : 6
Let boys = 7x
Girls = 5x
When 30 girls are added
Girls = 5x + 30
New ratio:
7x / (5x + 30) = 7 / 6
6 × 7x = 7(5x + 30)
42x = 35x + 210
7x = 210
x = 30
Number of boys = 7x = 7 × 30 = 210