2020 · Q41
A car did a journey in t hours. Had the average speed been x kmph greater, the journey would have taken y hours less. How long was the journey?
Elementary MathematicsTime, Speed and Distance
- Ax(t − y)ty
- Bx(t − y)ty⁻¹
- Cx(t − y)ty⁻²
- Dx(t + y)ty
Explanation
From vt = (v+x)(t-y) we get vy = x(t-y), so v = x(t-y)/y and the distance vt = x(t-y)t/y = x(t-y)ty^-1. Hence option (B). As a sanity check with t = 2, y = 1: v = x, D = 2x, and (x+x)*1 = 2x matches.