Here's how to subtract 4/10 from 2/7:


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 2 by 10, and get 20. Then we multiply 4 by 7, and get 28. Next we give both terms new denominators  7 × 10 = 70. So now our fractions look like this:


Step 2Since our denominators match, we can subtract the numerators. 20 − 28 = 8 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... Nope! So now we try the next greatest prime number, 3... Nope! So now we try the next greatest prime number, 5... No good. 5 is larger than 4. So we're done reducing. There you have it! The final answer is:
