Write a proportion of the two fractions, using x to represent the unknown numerator of the eighths.
Example:
How many eighths is 2/3?
2/3 = x/8
Cross-multiply, multiplying the right-hand numerator with the left-hand denominator and the right-hand denominator with the right-hand numerator. Write the two results as equal to one another.
Example:
2/3 = x/8
2*8 = x*3
16 = 3x
Divide both sides by the number in front of the x. Write this answer in sentence form.
Example:
16 = 3x
5.33... = x
2/3 is equal to 5.33.../8.