Question

Making use of the cube root table, find the cube root
34.2

Answer 1

The number 34.2 could be written as $\frac{342}{10}$.

Now

$\sqrt[3]{34.2}=\sqrt[3]{\frac{342}{10}}=\frac{\sqrt[3]{342}}{\sqrt[3]{10}}$

Also

$340<342<350\Rightarrow \sqrt[3]{340}<\sqrt[3]{342}<\sqrt[3]{350}$

From the cube root table, we have:

$\sqrt[3]{340}=6.980\text{and}\sqrt[3]{350}=7.047$

For the difference (350$-$340), i.e., 10, the difference in values

$=7.047-6.980=0.067$.

$\therefore$ For the difference (342$-$340), i.e., 2, the difference in values

$=\frac{0.067}{10}\times 2=0.013$ (upto three decimal places)

$\therefore$ $\sqrt[3]{342}=6.980+0.0134=6.993$ (upto three decimal places)

From the cube root table, we also have:

$\sqrt[3]{10}=2.154$

$\therefore$ $\sqrt[3]{34.2}=\frac{\sqrt[3]{342}}{\sqrt[3]{10}}=\frac{6.993}{2.154}=3.246$

Thus, the required cube root is 3.246.