A coin is placed 12.0 cm from the axis of a rotating turntable of variable speed. When the speed of the turntable is slowly increased, the coin remains fixed on the turntable until a rate of 37.0 rpm (revolutions per minute) is reached, at which point the coin slides off.

Explanation:

For the given situation,

          Frictional force = centripetal force

Cancel out the common terms, we get

                   =  (as 1 rpm = 0.10472 rad/sec)

                   =

                   = 0.183

thus, we can conclude that coefficient of static friction in the given situation is 0.183.

mistakes are ok

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