Trains Boats and Streams Practice Test 2 with solutions

Let usual speed of the train be x km/hr, then,
$\frac{200}{\mathit{x}-10}-\frac{200}{\mathit{x}}$ = $\frac{40}{60}$
⇒ $\frac{200\times 10}{{\mathit{x}}^2-10\mathit{x}}$ = $\frac{2}{3}$
⇒ ${\mathit{x}}^2-10\mathit{x}$ = $\frac{200\times 100\times 3}{2}$
⇒ ${\mathit{x}}^2$ – 10x – 3000 = 0
⇒ (x – 60) (x + 50) = 0
∴ x = 60 (Taking positive value)
Hence, speed of the train = 60 km/hr