Here's how to subtract 1/9 from 1/7:


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 1 by 9, and get 9. Then we multiply 1 by 7, and get 7. Next we give both terms new denominators  7 × 9 = 63. So now our fractions look like this:


Step 2Since our denominators match, we can subtract the numerators. 9 − 7 = 2 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... Nope! So now we try the next greatest prime number, 3... No good. 3 is larger than 2. So we're done reducing. There you have it! The final answer is:
