Question

Ali rides a bicylce for one hour
for the first 20 minutes his average speed is 18km/h
for the next 40 minutes his average speed is 15km/h
what is his overall average speed

A)16 km/h
B)16.5 km/h
C)17 km/h
D)17.5km/h

Answer 1

Answer:

the answer is 16km/hr

Explanation:

Ali rides the bicycle for 1 hour

average speed for 20minutes is 18km/hr

average Speed for 40 minutes is 15km/hr

Now we need to convert 20 minutes to hour

1 hour = 60 minutes.

therefore,

$20minutes = \frac{20}{60} = \frac{1}{3} hour$

$40minutes = \frac{40}{60} = \frac{2}{3} hour$

Now applying the formula

$speed = \frac{distance}{time}$

For 20 minutes distance will be

$18 \frac{km}{h} = \frac{distance}{ \frac{1}{3}hour } \\( 18 \times \frac{1}{3}) km = distance \\ 6km \: = distance \: covered \: for \: 20minutes$

For 40 minutes distance will be

$15 \frac{km}{h} = \frac{distance}{ \frac{2}{3}hour } \\( 15 \times \frac{2}{3}) km = distance \\ 10km \: = distance \: covered \: for \: 40minutes$

so total distance covered = (6+10) km = 16 km

Now to calculate average speed we apply the formula,

$Avg \: speed = \frac{distance}{time} \\ = \frac{16km}{1 \: hour} \\ = 16 \frac{km}{h}$

hope it helps.