When \(\frac{11}{2^8\cdot 5^5}\) is converted into \(\frac{N}{10^8}\), what is N?
Answer and explanation
Correct answer: 1375
Core idea: \(10^8=2^8\cdot 5^8\). The given denominator has \(2^8\) but only \(5^5\), so it is short by \(5^3\). Multiply numerator and denominator by \(5^3=125\) to obtain denominator \(10^8\). Thus \(N=11\times125=1375\).
Why other options are wrong: 275 equals \(11\times25\) (wrong if you multiply by \(5^2\) instead of \(5^3\)). 2750 is simply twice the correct N (a mistake from an extra factor 2). 6875 equals \(11\times625\) (would result from multiplying by \(5^4\)).
Exam tip: Compare prime-power factors of the denominator with \(10^n\); multiply numerator by the missing power of 2 or 5 to convert to denominator \(10^n\).
Frequently asked questions
What is the correct answer to this question?
1375
Why is this the correct answer?
Core idea: \(10^8=2^8\cdot 5^8\). The given denominator has \(2^8\) but only \(5^5\), so it is short by \(5^3\). Multiply numerator and denominator by \(5^3=125\) to obtain denominator \(10^8\). Thus \(N=11\times125=1375\).
Why other options are wrong: 275 equals \(11\times25\) (wrong if you multiply by \(5^2\) instead of \(5^3\)). 2750 is simply twice the correct N (a mistake from an extra factor 2). 6875 equals \(11\times625\) (would result from multiplying by \(5^4\)).
Exam tip: Compare prime-power factors of the denominator with \(10^n\); multiply numerator by the missing power of 2 or 5 to convert to denominator \(10^n\).
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Real Numbers. Topic: Decimal expansion of rational numbers.
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