Find the smallest number that when multiplied with a decimal will give a whole number

Question

Given a decimal number $x$ ($3.25$ for example), how would I find $y$ so that $x * y$ equals a whole number?

Answer 1

Take the decimal part and write it as a fraction. E.g. for 3.25, take the 0.25 and write it as $25/100$. Reduce it to lowest terms: $1/4$. The denominator will be the number you want. Another example, 5.222. Fractional part = $222/1000$. Reduce: $111/500$, so $500$ is the answer.

Answer 2

The common idea is to check how many digits are to the right of the decimal point. For each digit, multiply by $10$. For example here, $3.25$ has two digits, so you'd multiply by $10 \cdot 10 = 100$.