Question 1011058
. to travel from singapore to kuala lampur ,a distance kf 390km , motoridt finds that if he travels 6 km/h faster than its usual average speed,he will take 15 minutes less ti complete his usual journey . Calculate the usual avergae speed of the motorist
<pre>Let usual speed be S
Then hypothetical speed = S + 6
We then get the following TIME equation: {{{390/S = 390/(S + 6) + 15/60}}}_______{{{390/S = 390/(S + 6) + 1/4}}}
390(4)(S + 6) = 390S(4) + S(S + 6) -------- Multiplying by LCD, 4S(S + 6)
{{{1560S + 9360 = 1560S + S^2 + 6S}}}	
{{{S^2 + 6S + 1560S - 1560S - 9360 = 0}}}
{{{S^2 + 6S - 9360 = 0}}}	
Continue to solve for S, the usual speed, ignoring the negative (< 0) value for S