The ratio of the present age of father to that of son is 7:2. After 10 years their ages will be in the ratio of 9:4. The present ages of the father is 
  • a)
     35 years
  • b)
     40 years
  • c)
     30 years
  • d)
     25 years
Correct answer is option 'A'. Can you explain this answer?

CA Foundation Question

2 Answers
NANDINI WALIA answered Feb 21, 2020
Let father age be X and son age be Y. Then
X/Y = 7/2
2X = 7Y ..... (1)
After ten years ,
(X+10)/(Y+10) = 9/4
4(X+10) = 9(Y+10)
4X + 40 = 9Y + 90
4X = 9Y + 50
2×2X = 9Y + 50

putting the value to 2X by equation 1

2×7Y = 9Y + 50
14Y = 9Y + 50
5Y = 50
Y = 10
Son age is 10 years .

putting the value of Y in equation 1

2X = 7Y
X = 7/2Y
X = 7/2×10
X = 70/2
X = 35
Father age is 35.

Jaya Chatterjee answered Feb 06, 2020
Let father age be X and son age be Y. Then
X/Y = 7/2
2X = 7Y ..... (1)
After ten years ,
(X+10)/(Y+10) = 9/4
4(X+10) = 9(Y+10)
4X + 40 = 9Y + 90
4X = 9Y + 50
2×2X = 9Y + 50

putting the value to 2X by equation 1

2×7Y = 9Y + 50
14Y = 9Y + 50
5Y = 50
Y = 10
Son age is 10 years .

putting the value of Y in equation 1

2X = 7Y
X = 7/2Y
X = 7/2×10
X = 70/2
X = 35
Father age is 35.

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