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In figure three semicircles A, B and $C$ are drawn having diameters $3 cm$ each and a circle $D$ is drawn with diameter $4.5 cm .$ Find the cost of painting the shaded region at the rate of 25 paise per $cm 2$ .

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None of these

15.84

Km/hr

16.8

km/ hr

20

km/hr

answer is A.

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Detailed Solution

Given that, three semicircles A, B and

C

are drawn having diameters

3 cm

each and a circle

D

is drawn with diameter

4.5 cm .

We know that, the circumference of circle is

2 π r

.
Finding the radius of the wheel,

602 = 30 cm

Calculating the circumference of the wheel,

2 π r = 2 × 227 × 30

⇒ 227 × 60

⇒ 13207 cm

Distance covered in 1 revolution is

13207 cm .

Calculating the distance covered in 140 revolutions.

13207 × 100 = 26400 cm

⇒

264 m

⇒ 2641000 km

As 1 hour equals to 60 minutes, calculating the distance covered in 1 hour by computing the product of distance and time.

2641000 × 60 = 15.84 km / h r

Therefore, the speed per hour which boy is cycling is 15.84 km/hr
Hence the correct option is 1.

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