Probelm # 8. For a 3-digit positive integer abc, when c = 5, we have 23 such integers that is divisible by 15; when c = 0, we have 24 of these integers. Total should be 47 instead of 27.

Problem #17. The minutes hand should be the second hand.

Thanks to gubachi for pointing this out. I agreed with gubachi.

These two mistakes were made by the original question writers. We missed them. Sorry for the inconvenience.