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Solutions
Given:
The ratio of the present age Chinky and Minky = 4 ∶ 5
The present age of Chinky’s mother = (9/2) × Minky’s age 5 years ago
The present age of Minky’s mother = (7/3) × Chinky’s age after 3 year
Concept used:
Divide the age according to ratio.
Formulae used:
Average Age = Sum of total age/Total person
Calculations:
Let the present age of Chinky be 4x and Minky be 5x
5 year ago Minky’s age = 5x – 5
The present age of Chinky’s mother = (9/2) × Minky’s age 5 years ago
So, the present age of Chinky’s mother = (9/2) × (5x – 5)
⇒ (45x – 45)/2
After 15 years, Chinky’s mother age = ((45x – 45)/2) + 15
⇒ (45x – 15)/2
Chinky’s age after 3 years = 4x + 3
The present age of Minky’s mother = (7/3) × Chinky’s age after 3 year
So, the present age of Minky’s mother = (7/3) × (4x + 3)
⇒ (28x/3) + 7
After 15 years, Minky’s mother age = (28x/3) + 7 + 15
⇒ (28x + 66)/3
Total age of Chinky’s mother and Minky’s mother after 15 years = ((45x – 15)/2) + ((28x + 66)/3)
⇒ (135x – 45 + 56x + 132)/6
⇒ (191x + 87)/6
Average age of Chinky’s mother and Minky’s mother after 15 years = Sum of total age/Total person
⇒ (191x + 43)/(6 × 2)
⇒ (191x + 87)/12 = 55
⇒ 191x = 573
⇒ x = 3
The present age of Chinky = 4x = 4 × 3 = 12
The present age of Minky = 5x = 5 × 3 =15
The Difference between Chinky’s and Minky’s present age = 15 – 12 = 3 years
The Difference between Chinky’s and Minky’s present age is 3 years