Shortcut Trick
Total units in the ratio = 7 + 9 = 16 units.
Given Sum = 128, so 16 units = 128 → 1 unit = 128 ÷ 16 = 8.
First number = 7 × 8 = 56.
Second number = 9 × 8 = 72.
∴ The correct answer is 56, 72.
Alternate Method
Given: Ratio of two numbers = 7 : 9 and Sum of numbers = 128.
Formula Used: If a sum S is divided in the ratio a : b, then the parts are (a / (a + b)) × S and (b / (a + b)) × S.
⇒ Let the two numbers be 7x and 9x.
⇒ According to the question, 7x + 9x = 128
⇒ 16x = 128
⇒ x = 128 ÷ 16
⇒ x = 8
⇒ First Number = 7 × 8 = 56
⇒ Second Number = 9 × 8 = 72
∴ The correct answer is 56, 72.
Additional Information
Ratio Definition
A ratio is a comparison of two or more quantities of the same kind by division. For a : b, 'a' is called the antecedent and 'b' is the consequent.
Inverse Ratio
The inverse ratio of a : b is b : a. This is commonly used in speed-time and work-efficiency problems.
Compounded Ratio
For two ratios a : b and c : d, the compounded ratio is (a × c) : (b × d).
Proportion
When two ratios are equal, they are said to be in proportion (a : b :: c : d), implying the product of extremes equals the product of means (ad = bc).