Question: There were some snowflakes at first. It snowed an additional 4 snowflakes every 5 minutes. If there were 58 snowflakes after 1 hour, how many snowflakes were there at first? Think carefully first, then make a decision:
There are 60 / 5 = 12 5 - minute intervals in 1 hour. 12 * 4 = 48 snowflakes fell in 1 hour. There were 58 - 48 = 10 snowflakes at first. So the answer is 10.