In a class the number of boys and girls is in the ratio of 4 : 5. If 10 more boys join the class, the ratio of numbers of boys and girls become 6 : 5. How many girls there in the class?

20
30
25
Couldn't be determined

Correct Answer: 25

Explanation:

Let original number of boys = 4N and number of girls = 5N
According to the question
(4N + 10)/5N = 6/5
⇒ 30N = 20N + 50
⇒ 10N = 50
∴ N = 50/10 = 5
∴ Number of girls = 5N = 5 x 5 = 25

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