Question

If a train crosses a pole in 20 seconds and 120 meter platform in 30 seconds then what is train length

Answer 1

$Let \: the \: length \: of \: train \: be \: \: x \: meter \\ Then \: it's \: speed = \frac{x}{20} \\ \frac{x + 120}{ \frac{x}{20} } = 30 \\ 20x + 2400 = 30x \\ x = 240 \: m$