Q1
In direct proportion, when one quantity doubles, the other:
Aalso doubles
Bhalves
Cstays the same
Dbecomes zero
CBSEClass 8 (CBSE)MathematicsCh 7 · Topic 1
Understanding Direct Proportion
Learning to identify and solve problems involving direct proportion.
Core concept
A classic example: if 5 pens cost ₹50, then the cost per pen (₹10) remains constant, so 10 pens (double the quantity) cost ₹100 (double the price) — this constant ratio (cost/quantity = ₹10) is the defining feature of direct proportion. Recognising direct proportion situations in daily life — like cost versus quantity, distance versus time at constant speed, or ingredients versus servings in a recipe — helps solve many practical problems using simple ratio reasoning rather than complex formulas.
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• Direct proportion: two quantities increase/decrease together at the same constant rate (ratio).
• If one quantity doubles, the other (in direct proportion) also doubles.
• Example: 5 pens cost ₹50 (₹10/pen); 10 pens cost ₹100, maintaining the same ratio.
• Common direct proportion situations: cost vs quantity, distance vs time (constant speed).