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What is the value of the expression: 20×4÷2−10+5, if + and − are interchanged and × and ÷ are interchanged?
12
15
18
20
15
Rewrite the expression using the new signs first, then apply the BODMAS rule (Brackets, Of, Division, Multiplication, Addition, Subtraction) sequentially.
Rewrite the expression using the new signs first, then apply the BODMAS rule (Brackets, Of, Division, Multiplication, Addition, Subtraction) sequentially.
Apply sign substitutions
Given expression: 20 * 4 / 2 - 10 + 5. Interchanging * with / and - with +: 20 / 4 * 2 + 10−5.
Apply BODMAS order
First, perform division: 20 / 4 = 5. Now the expression is 5 * 2 + 10−5. Second, perform multiplication: 5 * 2 = 10. Now the expression is 10 + 10−5.
Final calculation
Add: 10 + 10 = 20. Subtract: 20 - 5 = 15.
A: Calculation error resulting from ignoring BODMAS order; C: Resulting from incorrect sign placement; D: Resulting from evaluating addition before multiplication.
B is correct because the application of BODMAS on the transformed expression 20 / 4 * 2 + 10−5 yields exactly 15.
Always write down the new expression clearly before performing any calculations to avoid confusion between the old and new symbols.