A. No, you cannot cross multiply when adding fractions. Cross multiply only when you need to determine if one fraction is greater than another, or if you are trying to find a missing numerator or denominator in equivalent fractions.

What is the rule of cross-multiplication?

In cross-multiplication, we multiply the numerator of the first fraction with the denominator of the second fraction and the numerator of the second fraction with the denominator of the first fraction.

Why is cross multiplying valid?

By comparing fractions using cross-multiplication, we lose the concept of finding equivalent fractions, which is ​why ​cross-multiplication works. ... This property states that if we multiply both sides of an equation or inequality by the same number, the values of each side remain equal.