Question

15. How long will a boy take to go four times round a circular field whose radius is 35 m, walking at 5 km per hour ?​

Answer 1

Question :-

How long will a boy take to go four times round a circular field whose radius is 35 m, walking at 5 km per hour?

Now,

Circumference of field = $2\pi r$

= $2$ × $\frac{22}{7}$ × $35$

= $2$ × $22$ × $5$

= $10$ × $22$

= $220$ $m$

Distance covered in 4 rounds = $220$ $m$ × $4$

= $880$ $m$

$Speed=5km/hr$

$=5000m/hr$

Thus,

$Time = \frac{Distance}{Speed}$

$=\frac{880}{5000}$ $hours$

$=\frac{88 }{500}$ $hours$

$=\frac{22}{125}$ $hours$

$=10.56$ $minutes$

Hence,

The time taken for a boy to take 4 rounds around a circular field whose radius is 35 m at 5 km per hr is $10.56$ $minutes$.

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Answer 2

Given:-

Radius of circular field = 35 m

Speed of the boy = 5 km/hr

Boy will have to four round around the circular field.

Solution:-

Circumference of the circular field ⇒ $2\pi r$

                                                         ⇒ 2 × $\dfrac{22}{7}$ × 35 m

                                                         ⇒ 220 m

Total Distance covered by boy to taking four round around the circular path ⇒ 220 m × 4  ⇔ 880 m

Now, Time taken by boy ⇒ $\dfrac{Distance}{Speed}$

                                         ⇒ $\dfrac{880 m}{5 km/hr}$              [ Distance is in Meter and speed is in Kilometer so we change one of them in Meter or in Kilometer ]

                                         ⇒ $\dfrac{880}{5000}$

                                         ⇒ 0.176 hour  or  10 minute 56 seconds

∴ Time taken by boy to travel four rounds of the circular field is 10 minute 56 seconds.

Some important terms:-

• 1 km = 1000 meter
• 1 meter = 100 centimeter
• 1 centimeter = 10 millimeter

• Distance = Speed × Time

• Circumference or Perimeter of Circle = $2\pi r$