Difficulty: Easy
Correct Answer: 5/18
Explanation:
Introduction / Context:
This problem asks you to convert a recurring (repeating) decimal into a vulgar fraction (a simple fraction in lowest terms). The decimal is written as 0.2(7), which means 0.2777… with only the 7 repeating endlessly. Understanding how to separate the non-repeating and repeating parts is the key skill tested here.
Given Data / Assumptions:
Concept / Approach:
Let x denote the repeating decimal. Use the standard technique: isolate the repeating part by shifting decimals using powers of 10. Because the repeating block has length 1 (only one digit repeats), multiplying by 10 moves the decimal one place; the non-repeating prefix (2) must be handled carefully. Subtracting two equations eliminates the repeating tail.
Step-by-Step Solution:
Let x = 0.2777…Multiply by 10 to shift one decimal place: 10x = 2.7777…Subtract: (10x − x) = 2.7777… − 0.2777… = 2.5Therefore 9x = 2.5, so x = 2.5 / 9 = 25/90 = 5/18.
Verification / Alternative check:
Convert 5/18 back to a decimal: 5 ÷ 18 = 0.2777…, which matches 0.2(7). The non-repeating digit 2 appears once, and the digit 7 repeats indefinitely, confirming correctness.
Why Other Options Are Wrong:
5/19 ≈ 0.263… (too small); 7/19 ≈ 0.368… (too large); 3/17 ≈ 0.176… (far too small); 7/25 = 0.28 (terminating, not recurring 7’s). Only 5/18 equals 0.2777…
Common Pitfalls:
Readers often treat 0.2(7) as if both digits 2 and 7 are repeating (i.e., 0.(27)), which is a different number. Always verify which digits are in the repeating block.
Final Answer:
5/18
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