Question:
The radius of a wheel is 0.25 m. How many revolutions will it make in covering 11 km?
(a) 2800
(b) 4000
(c) 5500
(d) 7000
Solution:
(d) 7000
Distance covered in 1 revolution $=2 \pi r$
$=\left(2 \times \frac{22}{7} \times 0.25\right) \mathrm{m}$
$=\left(2 \times \frac{22}{7} \times \frac{25}{100}\right) \mathrm{m}$
$=\frac{11}{7} \mathrm{~m}$
Number of revolutions taken to cover $11 \mathrm{~km}=\left(11 \times 1000 \times \frac{7}{11}\right)$
$=7000$
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