Find a common denominator is that when multiplying two we add/subtracted fractions for any numbers in the denominators have the same value. This would allow to add and subtract fractions easily, using only the numerators.
Example:6/7+4/5.Denominators do not match, so we need to find numbers that when you multiply them by each of the fractions would lead them to a common multiplier. For the first fraction is the number 5 and 7 for the second.
Now you need to multiply the numerator and denominator of each fraction to the corresponding multiplier. Turns out:30/35 + 28/35 = 58/35 = 1,657 (decimal)