Maths Olympiad Prep

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Algebra Difficulty 2.8 Junior Find the answer

Given that 2a=5b=102^{a}=5^{b}=10, find the value of 1a+1b=(    )\frac{1}{a}+\frac{1}{b}=(\ \ \ \ ).

Pick one

Solution

Since 2a=5b=102^{a}=5^{b}=10, we can write a=1log102a=\frac{1}{\log_{10}2} and b=1log105b=\frac{1}{\log_{10}5}.

Then,
1a+1b=log102+log105=log10(2×5)(Using the product rule for logarithms)=log10(10)=1 \begin{align} \frac{1}{a}+\frac{1}{b} &= \log_{10}2 + \log_{10}5 \\ &= \log_{10}(2 \times 5) &&\text{(Using the product rule for logarithms)} \\ &= \log_{10}(10) \\ &= 1 \end{align}

Therefore, the correct answer is (B) 1\boxed{(B)\ 1}.

This problem involves converting exponential equations to logarithmic form and applying the properties of logarithms. It is a basic question that tests one's understanding of these concepts.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.