8: 10-7: 50 You can first convert 8: 10 into the time starting from 7, which is 7: (10+60) = 7: 70.

7: 70-7: 50 = 20 minutes.

Extended data:

Conversion relationship of time units:

(1) One day = 1440 minutes, 1 hour =60 minutes, 1 minute =60 seconds.

(2) A moment = 15 minutes, and a word =5 minutes (used in southern Fujian and Guangdong).

Angle relation of each pointer of the clock:

(1) An ordinary clock is equivalent to a circle, and its hour hand or minute hand is equivalent to walking 360 degrees.

(2) The angle of each large grid on the clock is 30.

(3) The angle of the hour hand every 1 min should be 0.5.

(4) The angle of minute hand per 1 min should be: 6.