How would you subtract 4/7 from 15/21?

step 1: both fractions must have the same denominator. In this case, 7 is a factor of 21 so we can convert 7ths into 21ths by multiplying the top and bottom numbers by 3

4 12

7 x 3 21

step 2: complete the calculation.

15 12 3

21 - 21 = 21

Hi Lonie, first you would need to make the denominators the same. To do this find the common number for 7 and 21 which would be 21. In which case 15/21 stays the same. 4/7 would become 12/21 as you would multiply the top and bottom by 3. Finally simply calculate 15/21 - 12/21. The denominators stay the same (21). For the numerator, it is 15 - 12 =3.

The answer is 3/21

To subtract 2 fractions, the denominator (the bottom number of the fraction) of the two fractions need to be the same. This is calculated by finding a common multiple for the two numbers. In this case the common multiple is 21 (21 is divisible by 21, 21 is divisible by 21).

To change a fraction to have a different denominator. In this case change 4/7 to x/21. Find the number that is multiplied by 7 to give 21 (7 x ? = 21, ? = 3). This number is multiplied by to the numerator (4 x 3 = 12).

Now perform the subtraction 15/21- 12/21 . To calculate, take the numerators away from each other (15-12 = 3). The answer is 3/21.

This can be simplified by dividing both the numerator and denominator by 3. The answer is now 1/7.

ANS = 1/7