Here's how to subtract 2/5 from 4/8:


Step 1We can't subtract two fractions with different denominators. So you need to get a common denominator. To do this, you'll multiply the denominators times each other... but the numerators have to change, too. They get multiplied by the other term's denominator. So we multiply 4 by 5, and get 20. Then we multiply 2 by 8, and get 16. Next we give both terms new denominators  8 × 5 = 40. So now our fractions look like this:


Step 2Since our denominators match, we can subtract the numerators. 20 − 16 = 4 So the answer is:


Step 3Last of all, we need to simplify the fraction, if possible. Can it be reduced to a simpler fraction? To find out, we try dividing it by 2... Are both the numerator and the denominator evenly divisible by 2? Yes! So we reduce it:
Let's try dividing by 2 again... Are both the numerator and the denominator evenly divisible by 2? Yes! So we reduce it:
Let's try dividing by 2 again... No good. 2 is larger than 1. So we're done reducing. There you have it! The final answer is:
