1、

Start Time+Time = End Time

End Time-Start Time = Time

End Time-Time = Start Time

2, the calculation method of addition:

Appendix+Appendix = Sum

(1) and-addend = another addend.

(2) The sum of the positions of the commutative addend remains unchanged.

3, the calculation method of subtraction:

Negative-negative = difference

(1) Difference+Minus = Minus

(2) subtraction-difference = subtraction

0 plus any number equals any number.

4, small x multiple = big, big-small = multiple, big-small multiple = small.

5. Any number multiplied by 0 equals 0.

6. The circumference of a rectangle = (length+width) x 2, and the letter means c = (a+b) x 2.