Mixed fraction. `1 1/2 + 3/8=?`

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lemjay's profile pic

lemjay | High School Teacher | (Level 3) Senior Educator

Posted on

`1 1/2+3/8`

Note that we may re-write a mix fraction as `a b/c=a+b/c` .

`=1+1/2+3/8`

Then, let's consider adding the fractions first. Since the two fractions have unlike denominator,  express them using the LCD as their denominator. The LCD of 1/2 and 3/8 is 8. So, multiply 1/2 by 4/4.

`=1+1/2*4/4+3/8=1+4/8+3/8`

Now that the fractions have the same denominator, let's proceed to add.

`=1+7/8`

Since this is in the form `a b/c=a+b/c` , then

`=1 7/8`

Hence,  `1 1/2 + 3/8=1 7/8`  . 

steveschoen's profile pic

steveschoen | College Teacher | (Level 1) Associate Educator

Posted on

Hi, user2337842,

There are various ways to do these.  I prefer to do this.

Make the 1  1/2 an improper fraction

1  1/2 = 3/2

So, we have:

  3  +  3 .

  2      8

Then, determine the common denominator.  We can use 8 here, because we can multiply the first fraction by 4/4:

 3  *  4 +   3 .

 2       4       8

That gives us:

  12  +   3 .

   8        8

Adding the tops, keeping the bottoms the same, we get 15/8.

Many teachers want this in mixed number format.  So, 15/8 means 15 divided by 8.  That gives us 1 R7, or:

1  7/8

Good luck, useruser2337842.  I hope this helps.

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