There are six 40 Watt lamps in a classroom. On average, they are less than half an hour per day. How many watts of electricity can be saved in 30 days

There are six 40 Watt lamps in a classroom. On average, they are less than half an hour per day. How many watts of electricity can be saved in 30 days

6 * (40 / 2) * 30 = 3600W

A math problem:
There are 1200 light bulbs in a factory. Number them as 0-1199, record them as the original number, then remove the 3 times number of the light bulb, and number them as 0 -?, then remove the 3 times number of the light bulb, and then edit them again until the last light bulb is removed. Question: what is the original number of the last light bulb removed?
729 is a multiple of 3. It was brushed in the first round, so 729 is not right

An = n (n-1) / 2 plus 1
Take 49 and get 1177

How many hours can a 40 Watt lamp last?

One kilowatt hour is 1kW / h, that is to say, a 1kW electric appliance uses one kilowatt hour, and your lamp is 40W. So 1000 / 40 = 25 kilowatt hour