Find the number of wagons
An engine has a top speed
when no wagons are attached to it. The speed reduces when wagons are attached. The reduction (from
) is proportional to the square root of the total number of wagons attached.
We have an engine with wagons attached to it already, which can move at a particular speed. If 7 wagons are added to this, the speed reduces by 10 mph. If another 20 are added, the speed further reduces by 20 mph. Find the initial number of wagons .
The answer is 9.
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1 solution
s=k sqrtw ( equation 1), s-10=ksqrt(w+7) ( equation 2), s-30=ksqrt(w+27) ( equation 3) s= -30, k=-10, w=9