When there is a part missing in given fraction that is equals to some other fraction will be solved by cross multiplying the fractions.
In cross multiplication multiply the numerator of one fraction by denominator of second fraction and numerator of second fraction with denominator of first fraction and both terms will be equals to each other as we can define it by an example, if there are two fractions as a / b = c / d then according to principle of cross multiplication a * d = b * c.
We can also explain it by specifying some steps:
In first step write both fractions equals to each other as:
x / 10 = 5 / 25.
In next step multiply the numerator of first fraction that is 'x' with denominator of second fraction that is 25 means x * 25 and in same manner, multiply the denominator of first fraction by numerator of second one that is 10 * 5.
Equate both terms as x * 25 = 5 * 10.
In last step divide both expressions with same number. x * 25 / 25 = 5 * 10 / 25.
So we get answer x = 50 / 25 = 2 .
So in given fraction x / 10, missing value is x = 2.
We can also cross check the answer by putting obtained value in given fraction as 2 / 10 , on simplification we get 1 / 5 that is equals to 5 / 25 = 1 / 5.