A train travels 240 km at a uniform speed. If its speed had been 10 km/h more, it would have taken 1 hour less for the journey. What is the original speed of the train?

Explanation

Let speed be x. Then 240/x − 240/(x+10) = 1, so 2400 = x(x+10), giving x²+10x−2400=0, i.e. (x+60)(x−40)=0. So x=40. Check: 240/40=6 h, 240/50=4.8 h, a difference of 1.2 h, so recheck: 240/x−240/(x+10)=2400/(x(x+10)) =1 gives x(x+10)=2400; x=40 gives 2000, so x=48.99 is needed. Correct factorisation uses 2400=x²+10x, roots x=−55.. so this item is invalid.

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