Difficulty: Medium
Correct Answer: 5
Explanation:
Introduction:
This problem is a classic operator coding question from verbal reasoning. The familiar arithmetic symbols +, -, x, and ÷ are assigned new meanings. We must first decode the expression based on these new meanings, then evaluate it correctly using normal arithmetic precedence. The example tests careful reading and disciplined application of standard calculation rules.
Given Data / Assumptions:
The symbol meanings are redefined as:
1) "+" represents multiplication (times).
2) "-" represents addition (plus).
3) "x" represents division (divide).
4) "÷" represents subtraction (minus).
The given coded expression is 54 x 9 - 3 ÷ 4. After decoding the symbols, we assume the usual precedence of operations: division and multiplication first, followed by addition and subtraction from left to right.
Concept / Approach:
The key idea is to rewrite the entire expression with its true operations before attempting any calculation. Once we have a standard arithmetic expression, we simply apply BODMAS or PEMDAS. Many mistakes in these questions come from mixing the original and redefined meanings of the symbols, so a clean translation step is essential.
Step-by-Step Solution:
Step 1: Replace each symbol with its new meaning. The "x" stands for division, so 54 x 9 becomes 54 / 9.Step 2: The "-" symbol stands for addition, so - 3 becomes + 3.Step 3: The "÷" symbol stands for subtraction, so ÷ 4 becomes - 4.Step 4: The decoded expression is therefore 54 / 9 + 3 - 4.Step 5: Apply precedence rules. First, perform the division: 54 / 9 = 6.Step 6: Substitute this value to obtain 6 + 3 - 4.Step 7: Now perform addition and subtraction from left to right: 6 + 3 = 9, then 9 - 4 = 5.Step 8: The final result of the coded expression is 5.
Verification / Alternative check:
We can quickly recheck by repeating the translation: 54 divided by 9 plus 3 minus 4. Evaluating again gives 6 + 3 - 4 = 5. There is no alternative bracketing indicated in the question, so our calculation is consistent and complete.
Why Other Options Are Wrong:
The value 10 would arise if someone added 6 and 4 instead of subtracting. The value 8 might come from evaluating 54 / 9 first, then doing 6 + (3 - 1) due to a misread of the operations. The value 2 could come from incorrectly grouping as 54 / 9 + (3 - 5). None of these follow the correct translation and precedence in a systematic way.
Common Pitfalls:
Students often forget to change all the operators before starting the calculation, or they unconsciously treat the symbols according to their usual meanings. Another common error is to perform the operations strictly from left to right, ignoring that division must be done before addition and subtraction. Writing the decoded expression clearly on paper helps avoid these mistakes.
Final Answer:
After decoding and evaluating, the value of the expression is 5.
Discussion & Comments