Put it on the second ring, the fourth ring and fold it in half. Open rings 2 and 4 simultaneously. It takes two minutes.

Put 1 on ring 2 and 5 on ring 4. It takes two minutes to close both rings 2 and 4.

* * * It will take 5 minutes.

For example:

A * * * five chains, connect these five chains into a chain, the first chain needs to be opened first, which takes two minutes, the second chain needs to be put in, and then the chain needs to be closed, which takes three minutes, and a * * * needs five minutes. Five chains * * * cost 5 times 5, and one * * * costs 25 points. The last chain doesn't need to be opened. Minus 5 points is 25 minus 5 plus 20 points.

When writing a math problem, write 2+3=5 (points) 5 times 5=25 (points) 25-5=20 (points).

Extended data:

(1) from the high order of dividend;

(2) How many digits is the divisor? Look at the first few digits of the divisor first. If it's not enough, look at one more digit.

(3) In addition to which one, which one to write the business on;

(4) The remainder of each division must be less than the divisor;

(5) If the quotient of 1 is not enough in dividend after finding the highest bit of quotient, write 0 on it;

Baidu encyclopedia-four operations