Shortcut Trick
Total sum of ratio parts = 4 + 3 = 7 parts.
Given 7 parts = 49 years ⇒ 1 part = 7 years.
Current ages: Sonu = 4 × 7 = 28 years, Bulla = 3 × 7 = 21 years.
Ages after 4 years: Sonu = 28 + 4 = 32 years, Bulla = 21 + 4 = 25 years.
Required ratio = 32 : 25.
∴ The correct answer is 32 : 25.
Alternate Method
Given:
⇒ Ratio of current ages of Sonu and Bulla = 4 : 3
⇒ Sum of their current ages = 49 years
Concept Used:
If two numbers are in the ratio a : b, they can be expressed as ax and bx, where x is a common multiplier.
Current Sum = 49 years (4x + 3x)
Sonu
28 yrs (4 parts)
+4 yrs
32 yrs
Bulla
21 yrs (3 parts)
+4 yrs
25 yrs
New Ratio = 32 : 25
Calculations:
⇒ Let Sonu's current age be 4x and Bulla's current age be 3x.
⇒ Sum of ages = 4x + 3x = 49
⇒ 7x = 49
⇒ x = 7
⇒ Sonu's current age = 4 × 7 = 28 years
⇒ Bulla's current age = 3 × 7 = 21 years
⇒ Sonu's age after 4 years = 28 + 4 = 32 years
⇒ Bulla's age after 4 years = 21 + 4 = 25 years
⇒ Ratio of their ages after 4 years = 32 : 25
∴ The correct answer is 32 : 25.
Additional Information
Compound Ratio
When two or more ratios are multiplied together, it is known as a compound ratio. For ratios a : b and c : d, the compound ratio is ac : bd.
Duplicate Ratio
The ratio of the squares of two numbers is called their duplicate ratio. For a given ratio a : b, its duplicate ratio is a2 : b2.
Invertendo (Inverse Ratio)
If a : b = c : d, then by the invertendo property, b : a = d : c. This is highly useful for reversing proportional relationships.
Age Constant Difference Rule
The age difference between any two people always remains constant over time. If their ages change by the same number of years, balancing the ratio difference solves cross-multiplication cases instantly.