Question 20.

Speed of John = 6 kmph 

Speed of Mary = 7.5 kmph 

Lengths of tracks A and B = 325 m

Let the length of track A be a, then the length of track B = 325-a

9 rounds of John on track A = 5 rounds of Mary on track B

$\frac{9 \times a}{6 × \frac{5}{18}}$ = $\frac{5 \cdot (325-a) }{7.5 × \frac{5}{18}}$

On solving we get , 13a=1300

a=100

The length of track A = 100m, track B = 225m

Mary makes one round of track A =   $\frac{100}{7.5 × \frac{5}{18}}$

= 48 sec