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Here are some tips for Missing Operator, which aligns with California state standards:

Missing Operator


To master this topic, you need to first master the topics:

There are two ways to solve missing operator problems.

First Method: Brute force

Supply the missing operator.      
10 = 3 7		 Supply the missing operator.
15 5 = 3
Try:   Try:  
  10 = 3 + 7? Yes!       15 + 5 = 3? No
  10 = 3 - 7? No   15 - 5 = 3? No
  10 = 3 × 7? No   15 × 5 = 3? No
  10 = 3 ÷ 7? No   15 ÷ 5 = 3? Yes!
Answer:   Answer:  
10 = 3 7   15 5 = 3  


Second Method: Using logic

Consider the problem in terms of three numbers: two operands and one answer.
  operand 1 operator operand 2 = answer
  3 × 7 = 21


  Supply the missing operator.
3 = 12 9		 Supply the missing operator.
6 3 = 18
Step 1: Compare operand 1 and answer
  If operand 1 is larger than the answer,
then the operation is either subtraction or division.

Since 12 > 3, the operation is either subtraction or division.		 If the operand 1 is smaller than the answer,
then the operation is either addition or multiplication.

Since 6 < 18, the operation is either addition or multiplication.
Step 2: Try the two operators
 
3 = 12 - 9? Yes!
3 = 12 ÷ 9? No
6 + 3 = 18? No
6 × 3 = 18? Yes!
Answer: 3 = 12 9 6 3 = 18

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