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.