Question 1171220
A delivery truck follows a regular route that is 270 km. One day the driver begins the route half hour late. In order to finish on time, she drives the truck 6km/hr faster than usual. What is the truck's usual speed
<pre>Let truck's normal speed be S
Then usual time = {{{270/S}}}
We then get the following TIME equation: {{{matrix(1,3, 270/S, "=", 270/(S + 6) + 1/2)}}}
270(2)(S + 6) = 270(2S) + S(S + 6) ------ Multiplying by LCD, 2S(S + 6)
{{{matrix(3,3, 540S + "3,240", "=", 540S + S^2 + 6S, S^2 + 540S + 6S - 540S - "3,240", "=", 0, S^2 + 6S - "3,240", "=", 0)}}}
(S - 54)(S + 60) = 0
Normal speed of truck, or {{{highlight_green(matrix(1,4, S, "=", 54, mph))}}}         OR          S = - 60 (ignore)