Shortcut Trick
Initial difference between the greater and smaller number = 5.
By adding 20 to the greater and subtracting 25 from the smaller, the new difference becomes: 5 + 20 − (−25) = 50.
The new ratio is 1 : 2, so the difference in ratio parts = 2 − 1 = 1 part.
Since 1 part = 50, the new greater number (which corresponds to 2 parts) = 2 × 50 = 100.
Original greater number = 100 − 20 = 80.
∴ The correct answer is 80.
Alternate Method
Given:
Difference between two numbers = 5
When 25 is subtracted from the smaller and 20 is added to the greater, the ratio becomes 1 : 2.
Formula Used:
Linear equations and ratio proportion concepts.
Smaller Number
Greater Number
x
x + 5
− 25
x − 25
x + 25
Ratio 1 : 2
Equation: (x − 25) / (x + 25) = 1 / 2
Calculations:
⇒ Let the smaller number be x.
⇒ Then, the greater number = x + 5
⇒ New smaller number = x − 25
⇒ New greater number = (x + 5) + 20 = x + 25
⇒ According to the question, the ratio becomes 1 : 2
⇒ (x − 25) / (x + 25) = 1 / 2
⇒ 2 × (x − 25) = 1 × (x + 25)
⇒ 2x − 50 = x + 25
⇒ 2x − x = 25 + 50
⇒ x = 75
⇒ The greater number = x + 5 = 75 + 5 = 80
∴ The correct answer is 80.
Additional Information
Ratio & Proportion Basics
When two quantities are in the ratio a : b, they can be represented as ax and bx, where x is a common multiplier.
Constant Difference Method
If the same value is added or subtracted to both parts of a ratio, the difference between the two numbers remains constant. This is highly useful in age-related problems.
Cross-Multiplication Method
For equations of the form a / b = c / d, the variables can be easily solved using cross-multiplication: a × d = b × c.