The approximate value of $\log _{10} 1002$ is (Given $\log _{10} \mathrm{e}=0.4343$ )

The approximate value of $\log _{10} 1002$ is (Given $\log _{10} \mathrm{e}=0.4343$ )
  1. 3.0117
  2. 3.0009
  3. 2.9999
  4. 3.1119

Solution

$\begin{aligned} & \text { Let } \mathrm{f}(x)=\log _e x \\ & \therefore \quad \mathrm{f}^{\prime}(x)=\frac{1}{x} \\ & \text { Here, } a=1000, \mathrm{~h}=2 \\ & \therefore \quad \mathrm{f}(\mathrm{a}+\mathrm{h}) \approx \mathrm{f}(\mathrm{a})+\mathrm{hf}^{\prime}(\mathrm{a}) \\ & \approx f(1000)+2 f^{\prime}(1000) \\ & \approx \log _{\mathrm{e}} 10^3+2 \times \frac{1}{1000} \\ & \approx 3(0.4343)+0.002 \\ & \approx 1.3029+0.002 \\ & \approx 1.3049 \\ & \therefore \quad \log _{\mathrm{e}} 1002 \approx 1.3049 \\ & \text { Now, } \log _{10} 1002 \approx \frac{\log _{\mathrm{e}} 1002}{\log _{\mathrm{e}} 10} \\ & \approx \frac{1.3049}{0.4343} \approx 3.0009 \end{aligned}$

Asked in: MHT CET 2024 (04 May Shift 1)

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