A train is moving at 15ms-1. It slows down to 10.5ms over a time of 4s. Calculate the distance it travels before stopping if acceleration is constant.

(v2 - v1) / t = a for uniform acceleration

a = (10.5 - 15) / 4 = -1.125 m / s^2

T = 15 / 1.125 = 13.3 s      time for train to stop from 15 m/s

S = V0 T + 1/2 a T^2

S = 15 * 13.3 - 1.125 / 2 * 13.3^2

S = 199.5 - 99.5 = 100 m

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form