Question

A train length 180mts moving with uniform speed cross a telephone pole in 18 secs .due to detachmentof some coaches its length reduced to 150mts

Answer 1

$speed = length \div time \\ length = 180mts. \: \: time = 18secs \\ speed=180 \div 18 = 10mt \div second. \\ time = length \div speed \\ length = 150. \: speed = 10 \\ time = 150 \div 10 = 15second.$