What should come in place of the question mark (?) in the following calculation, if you apply the correct order of operations? 600 + 300 ÷ 15 = ? × 31

Introduction / Context:
This question tests understanding of the order of operations in an equation that links an arithmetic expression on the left to a product on the right. The learner must simplify the left hand side correctly and then solve for the unknown multiplier that appears on the right side.

Given Data / Assumptions:
- Equation: 600 + 300 ÷ 15 = ? × 31. - Division is done before addition. - Multiplication by 31 happens after the left side is simplified.

Concept / Approach:
According to the order of operations, division precedes addition. Thus we first divide 300 by 15, then add the result to 600. Once the left side is fully evaluated, we equate it to 31 times the unknown number and solve a simple linear equation to find that number.

Step-by-Step Solution:
Step 1: Evaluate 300 ÷ 15 = 20. Step 2: Add this result to 600: 600 + 20 = 620. Step 3: The equation becomes 620 = ? × 31. Step 4: Solve for the unknown: ? = 620 ÷ 31. Step 5: Compute 620 ÷ 31 = 20.

Verification / Alternative check:
Substitute 20 back into the right side to verify: 20 × 31 = 620. This matches the simplified left side value 620. Since both sides are equal, the value 20 satisfies the equation and is therefore correct.

Why Other Options Are Wrong:
- Option 18 gives 18 × 31 = 558, which is less than 620. - Option 25 gives 25 × 31 = 775, which is greater than 620. - Option 40 gives 40 × 31 = 1240, which also does not equal 620.

Common Pitfalls:
A typical mistake is to add first and divide later, which would change the left side value. Another error is miscalculating 300 ÷ 15 or the final division by 31. Sticking closely to the order of operations and checking each step avoids these mistakes.

Final Answer:
The value that satisfies the equation is 20, so the correct option is 20.