Question

Find the first term of a proportion whose second, third, and fourth terms are $5,15$ and $25$, respectively.

Answer 1

Finding the first term of the given proportion:

Let the first term of the given proportion is $X$.

As we have given the second, third, and fourth terms are $5,15$ and $25$.

so, we can write it as $X:5::15:25$

Now, we know that when the two ratios form proportion then the given ratios are equal.

Using that we have,

$$\begin{gathered} \Rightarrow \frac{X}{5}=\frac{15}{25} \\ \Rightarrow X=\frac{15\times 5}{25}(Cross-Multiplication) \\ \Rightarrow X=\frac{5\times 3\times 5}{5\times 5} \\ \Rightarrow X=3 \end{gathered}$$

Hence, the first term of the given proportion is $3$.