Question 1042715

a car travels at a constant speed for 450km if the average speed was increased by 15km/h the journey would have taken 90 min less find speed of car
<pre>Let speed of car be S
Then hypothetical speed = S + 15
We then get the following TIME equation: {{{450/S = 450/(S + 15) + 90/60}}}_____{{{450/S = 450/(S + 15) + 3/2}}}
450(2)(S + 15) = 450(2S) + 3S(S + 15) --------- Multiplying by LCD, 2S(S + 15) 
{{{900S + "13,500" = 900S + 3S^2 + 45S}}}
{{{3S^2 + 900S + 45S - 900S - "13,500" = 0}}} ======> {{{S^2 + 15S - "4,500" = 0}}}
Factor the trinomial on the left to solve for S: the speed of the car. You should get {{{highlight_green(matrix(1,2, 60,km/h))}}}