The time, t, required to drive a fixed distance varies inversely as the speed, r. It takes 9 hr at a speed of 20 km/h to drive a fixed distance. How long will it take to drive the same distance at a speed of 23 km/h?

Time=7.84hrs

Explanation:

This is an inverse proportionality questions

Mathematically time t varies as 1/distance d

Hence T = dk/r

But speed r = distance/t

d = r*t = 9*20=180km/hr

We're k = constant of proportionality

At t=9hrs d=180km/hr

Hence k=r*t/d=20*9/1620=0.111

Finding t at at 1620km for 23km/hr

t=1620*0.111/23=7.84hrs