Question

The ratio of Wei Ling's age to Wei Xuan's age 5 years ago was 2: 5. In 9 years

time, the ratio of Welling's age to Wel Xuan's age will be 3:4 How old is Wei
Xuan now?

Answer 1

15 years old

Explanation:

Start by defining the variables that we are going to use throughout our working:

Let the current age of Wei Ling and Wei Xuan be L and X years old respectively.

Next, form equations using the given information.

5 years ago

Wei Ling: (L -5) years old

Wei Xuan: (X -5) years old

Given that the ratio of Wei Ling's age to that of Wei Xuan's is 2: 5,

`( L - 5)/(X - 5) = (2)/(5)`

Cross multiply:

2(X -5)= 5(L -5)

Expand:

2X -10= 5L -25

2X= 5L -25 +10

2X= 5L -15 -----(1)

9 years time

Wei Ling: (L +9) years old

Wei Xuan: (X +9) years old

Given that the ratio of Wei Ling's age to that of Wei Xuan is 3: 4,

`(L + 9)/(X + 9) = (3)/(4)`

Cross multiply:

3(X +9)= 4(L +9)

Expand:

3X +27= 4L +36

3X= 4L +36 -27

3X= 4L +9 -----(2)

Let's solve using the elimination method.

(1) ×3:

6X= 15L -45 -----(3)

(2) ×2:

6X= 8L +18 -----(4)

(3) -(4):

6X -6X= 15L -45 -(8L +18)

0= 15L -45 -8L -18

0= 7L -63

7L= 63

L= 63 ÷7

L= 9

Substitute L= 9 into (1):

2X= 5(9) -15

2X= 45 -15

2X= 30

X= 30 ÷2

X= 15

Thus, Wei Xuan is 15 years old now.