Nail two boards of the same length together, just one meter long. The overlap of the two boards is 30 cm long. How long are the two boards?

Nail two boards of the same length together, just one meter long. The overlap of the two boards is 30 cm long. How long are the two boards?

The answer is that the 65cm overlap counts twice, so it's 100 plus 30 divided by two

Cut a 6-meter-long rectangular steel into two sections, and the surface area will increase by 50 square centimeters. What is the original volume of this steel?

Cross section = 50 △ 2 = 25 square centimeter
6m = 600cm
Volume = 25 × 600 = 15000 CC

How often do you feed a small goldfish (2 to 3 cm long) at 5 jiao? How often do you change the water?

What's your current water temperature? Generally, it's OK to feed once a day when the water temperature is 15-20 degrees, around 17:00 in the afternoon, twice a day when the water temperature is 20-25 degrees, once at 8:00 in the morning and once at 18:00 in the afternoon. The quantity of each feeding should not be too much. It's better to eat it in 15 minutes. The problem of changing water depends on how many fish you raise in a large area. If there are not many fish, you usually change the water once a week, Before changing water, if it is tap water, it should be aerated. The method of aeration is: put the water into a clean bucket for more than 24 hours, so as to discharge the chlorine from the water. After 24 hours, the water can be changed