Here's how to subtract 7/8 from 9/12:


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 9 by 8, and get 72. Then we multiply 7 by 12, and get 84. Next we give both terms new denominators  12 × 8 = 96. So now our fractions look like this:


Step 2Since our denominators match, we can subtract the numerators. 72 − 84 = 12 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... Nope! So now we try the next greatest prime number, 3... Are both the numerator and the denominator evenly divisible by 3? Yes! So we reduce it:
Let's try dividing by 3 again... No good. 3 is larger than 1. So we're done reducing. There you have it! The final answer is:
