Question 1149780
Hi

a student was driving to school at 50mph. A quarter of the way he ran out of petrol. If he ran the rest of the way at 10mph what was his average speed.

thank you
<pre>With the student driving {{{1/4}}} of the distance, and at 50 mph, time spent driving = {{{matrix(1,7, ((1/4) * D)/50, "=", (D/4)/50, "=", (D/4) * (1/50), "=", D/200)}}}
With the student running {{{3/4}}} of the distance, and at 10 mph, time spent running = {{{matrix(1,7, ((3/4) * D)/10, "=", (3D/4)/10, "=", (3D/4) * (1/10), "=", 3D/40)}}}
Average Speed = {{{matrix(1,2, Total, distance)/matrix(1,2, Total, Time)}}}
Average Speed = {{{D/(D/200 + 3D/40)}}}, with D being total distance
{{{highlight_green(matrix(1,14, Average, speed, "=", D/((D + 15D)/200), "=", D/(16D/200), "=", D * (200/(16D)), "=", cross(D) * (25cross(200)/2cross(16)cross(D)), "=", 25/2, "=", highlight(matrix(1,2,12.5, mph)))))}}}