Q1. [1] § Chapter Opening and Epigraph
A bag contains red balls and black balls in the ratio 3 : 7. A ball is drawn at random. The probability that ball so drawn is black in colour, is
- A $\frac{3}{7}$
- B 0.3
- C 0.7
- D $\frac{1}{7}$
Previously asked in CBSE board exam
2025 30/5/1 Q7
Generated by claude-sonnet-4-6 · 2026-06-15 10:31 · grounding rag
Model Answer
Option C: 0.7
Ratio of red : black = 3 : 7, so total parts = 10. P(black) = 7/10 = 0.7.
Source: Chapter 14, Section 14.1
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Explanation
Total balls = 3 + 7 = 10 parts. Favourable outcomes (black) = 7. P(black) = 7/10 = 0.7. Note that 3/7 is the ratio of red to black, not a probability — a common mistake to avoid.
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