Adding and subtracting fractions
If the denominators (the bottom numbers) are the same, we just need to add or subtract the numerators (the top numbers).
$$5/7+1/7=6/7$$
$$4/9−3/9=1/9$$
If the denominators (the bottom numbers) are different, we need to find the least common denominator. We can do this by following these steps:
$$1/4+1/2$$
Step 1: Convert fractions to have the same denominator (by multiplying):
$$1/4+1/2×2/2=1/4+2/4$$
Step 2: Add or subtract the numerators (the top numbers), and write the result over the same denominator (the bottom number).
$$1/4+2/4=3/4$$
Sometimes is better to divide one of the fractions:
$$4/6+2/3={4÷2}/{6÷2}+2/3=2/3+2/3=4/3$$
And in some cases you have to cross-multiply (multiply the numerator of each fraction by the denominator of the other):
$$4/7−1/3=4/7×3/3−1/3×7/7=$$
$$=12/21−7/21=5/21 $$
If you are adding/subtracting fractions and whole numbers, you can turn the whole number into a fraction with the same denominator.
$$1/5+1=?$$
$$1=1/1=2/2=3/3=4/4=5/5$$
$$;→;1/5+5/5=6/5$$
$$13/3−4=?$$
$$4=4/1=8/2=12/3;→;13/3−12/3=1/3$$
