In a 100m race, a sprinter accelerates for the first 40.0m at 2.56m/s^2. After this distance he reaches the top speed and maintains this speed for the rest of the race. How long did it take the sprinter to run the first 40m of the race?

total distance (dtot) = 100m

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first 40 meters (d1) = 40m

a = 2.56 m/s^2

Let's calculate this part first. We need the time.

s = 1/2 * a * t^2

t = = = = 5,5 s (circa)

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