alleryA roller of diameter 84 cm and length 1 m turns 750 times. Area levelled (pi = 22/7)?
A990 m2
B3960 m2
C1980 m2
D2640 m2
Answer & Solution
Correct answer: C. 1980 m2
1. One turn covers the curved surface 2πrh = 2 × (22/7) × 0.42 × 1 = 2.64 m2.
2. 750 turns cover 750 × 2.64 = 1980 m2.
3. Using the diameter as r would give 3960 m2 wrongly.
_Source: NCERT Class 8 Mathematics, Chapter 9 Mensuration, Exercise 9.2_
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