Question

P.T. Usha runs around a circular path of area 754600 sq meter. How long will she take to run 20 rounds at the speed of 16 km/hr.

Answer 1

Area of circle = 754600 sq m.
$=\pi \times r^2$
Hence, radius of circle =$\sqrt{\left(\frac{A}{\pi }\right)}=\sqrt{(754600\times \frac{7}{22})}$
$=\sqrt{(34300\times 7)}=\sqrt{\left(240100\right)}$
$=\sqrt{(2401\times 100)}$
$=10\times 49=490m.$
Now, the circumference of this circle $=2\pi r=2\times \frac{22}{7}\times 490=2\times 22\times 70=3080m.=3.08km.$
P T Usha runs 20 rounds = $20\times 3.08=61.6km$
Her speed is 16 km/hr $\to$ time taken to complete 61.6 km = $\frac{61.6km}{16km/hr}$ = 3.85 hrs.