Find the missing value.

Main drive gear = 45 teeth

Speed of main drive gear = 450 r. p. m.

Countershaft drive gear = 70 teeth

Speed of countershaft drive gear (to the nearest tenth) = ? r. p. m.

To calculate the speed of the 70 teeth countershaft drive gear, evaluate the surface teeth per minute (STM) of each gear. STM = Speed x number of teeth, which is equivalent for both gears. Thus, 45 teeth * 450 r. p. m. = 70 teeth * 'x' r. p. m. is the governing equation. Rearranging the equation to calculate 'x' as the 70 teeth gear's speed, the answer is 289.3 r. p. m.