Question

Running Exercise
The doctor has told Devi Prasad to run 2 km every day to stay fit. He took one round of this field. How far did he run?
The field was very far from his home. So he chose a park nearby. The boundary of the park was about 400 metres long.
• How many rounds of the park must Devi Prasad run to complete 2 km?

• One day the weather was very good and a cool breeze was blowing. He felt so good that he kept jogging till he got tired after 8 rounds. That day he ran ___________ km and __________ metres !

Answer 1

• Devi Prasad took 1 round of the square field whose each side was 500 m long.
Distance covered to take 1 round of the field = (500 + 500 + 500 + 500) m
= 2000 m
We know
1000 m = 1 km
Thus,
2000 m = 2 km
So, Devi Prasad ran 2 km to take one round of the field as advised by the doctor.
Length of the boundary of the park = 400 m
Number of rounds of the park taken by Devi Prasad to run 400 m = 1

Number of rounds of the park taken by Devi Prasad to run 1 m = $\frac{1}{400}$

Number of rounds of the park taken by Devi Prasad to run 2000 m = $\frac{1}{400}\times 2000$
= $2000÷400$
= 5
We know
2000 m = 2 km
So, Devi Prasad must take 5 rounds in order to complete 2 km.

• Distance covered by Devi Prasad to take 1 round of the park = 400 m
∴ Distance covered by Devi Prasad to take 8 rounds of the park = $400\mathrm{m}\times 8$
= 3200 m
We know
1000 m = 1 km
∴ 3200 m = 3000 m + 200 m
3200 m = 3 km + 200 m
3200 m = 3 km 200 m
Thus, Devi Prasad ran 3 km 200 m to take 8 rounds of the park.