Application of multiplication and distribution laws;
① type 1: (a+b)×c (a-b) ×c
= a× c + b×c = a× c - b×c
② the second category: a× c+b× c a× c–b× c.
=(a + b)× c =(a - b) × c
③ Type Ⅲ: A× 99+A× B-A.
= a ×(99 + 1) = a ×(b - 1)
④ Type IV: a × 99 a × 102.
= a×( 100- 1)= a×( 100+2)
Simple calculation of 1, continuous addition: ① Using the law of additive combination (combining the sum of whole ten, whole hundred and whole thousand with sum).
② Positions: 1 and 9,2 and 8,3 and 7,4 and 6,5 and 5, combined.
③ Decimal digits: 0 and 9, 1 and 8, 2 and 7, 3 and 6, 4 and 5, combined.
2. Simple calculation of continuous reduction:
Subtracting several numbers in a row is equal to subtracting the sum of these numbers. Such as:106-26-74 =106-(26+74)
② Subtracting the sum of several numbers is equivalent to subtracting these numbers continuously. Such as:106-(26+74) =106-26-74.
3. Simple calculation of addition and subtraction:
The position of the first number remains the same, and other addends and subtractions can be interchanged (you can add first and then subtract).
For example:123+38-23 =123-23+38146-78+54 =146+54-78.
= a× 100–a× 1 = a× 100+a×2