Question 947651
 a car travelled 25km at an average speed of xkm\h.if its speed was increased by 5km\h it covers the distance 15minutes earlier what is the original speed of car?
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At least he/she was honest about his/her inability to solve this problem!!

With average speed being x, time taken to travel 25 km = {{{25/x}}}
Increasing speed by 5 km/h means that its speed becomes: x + 5
Time taken to cover distance at new speed of x + 5: {{{25/(x + 5)}}}
We then get: {{{25/x = 25/(x + 5) + 15/60}}}, which becomes: {{{25/x = 25/(x + 5) + 1/4}}}
25(4)(x + 5) = 25(4x) + x(x + 5) -------- Multiplying by LCD, 4x(x + 5)
{{{100x + 500 = 100x + x^2 + 5x}}}
{{{x^2 + 5x + 100x - 100x - 500 = 0}}}
{{{x^2 + 5x - 500 = 0}}}
(x - 20)(x + 25) = 0
x, or original speed = {{{highlight_green(20)}}} km/h	         OR           x = - 25 (ignore)