Question

The ages of JingJing and her cousin are in the ratio of 4 : 7. In 5 years time, their ages will be in the ratio of 3: 5 How old is JingJing in 5 years time?

Answer 1

45 years old

Explanation:

In this question, we have the present ratios of two cousins. Given their ratios is the next five years, we are asked to calculate what the age of Jingjin who is one of the cousins would be in the next five years.

Now, let’s look at their present ratio;

4:7

or we can just say let Jinngjin’s age be j and his cousin’s c presently

4:7 = j:c

4/7 = j/c

4c = 7j •••••••(i)

now in the next five, their ratio will be 3 to 5

mathematically, that is expressed as;

j+5:c+5 = 3:5

(j+5)/(c+5) = 3/5

5(j+5) = 3(c+5)

5j + 25 = 3c + 15

3c - 5j = 10. •••••(ii)

From 2 we can say c = (10+5j)/3

let’s put this into 1, we have;

4[(10+5j)/3] = 7j

40 + 20j = 21j

j = 40

In the next 5 years , j will be 40 + 5 = 45 years old