Question

Question 11:

Answer 1

Answer:

69 miles per hour

Step-by-step explanation:

Given

Trip to:

$t_1 = 6$ --- time

$s_1 = 23 + s_2$

Trip back

$t_2 = 9$

Required

Determine the average speed to Johannesburg

Average speed is calculated as:

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

Make distance the subject

$distance = speed * time$

Since distance is constant, then:

$s_1 * t_1 = s_2 * t_2$

This gives:

$(23 + s_2) * 6 = s_2 * 9$

Open bracket

$138 + 6s_2 = 9s_2$

Collect like terms

$9s_2 - 6s_2 = 138$

$3s_2 = 138$

Solve for s2

$s_2 = 138/3$

$s_2 = 46$

Recall that:

$s_1 = 23 + s_2$

$s_1 = 23 + 46$

$s_1 = 69$