17. | How many times do the hands of a clock coincide in a day? | |||||||

The hands of a clock coincide 11 times in every 12 hours (Since between 11 and 1, they coincide only once,
12:00
12:00 The hands overlap about every 65 minutes, not every 60 minutes. The hands coincide 22 times in a day. |

18. | How many times in a day, the hands of a clock are straight? | |||||||

In 12 hours, the hands coincide or are in opposite direction 22 times. In 24 hours, the hands coincide or are in opposite direction 44 times a day. |

19. | A watch which gains uniformly is 2 minutes low at noon on Monday and is 4 min. 48 sec fast at 2 p.m. on the following Monday. When was it correct? | |||||||||||||||||||||||||||||

Time from 12 p.m. on Monday to 2 p.m. on the following Monday = 7 days 2 hours = 170 hours.
Watch is correct 2 days 2 hrs. after 12 p.m. on Monday |