Adding and Subtracting Fractions

  • 格式:dps
  • 大小:252.00 KB
  • 文档页数:10

Adding and Subtracting
Fractions
By Graeme Henchel
8
3
Adding Fractions with common denominators
8483
+87=/ 天津塔吊租赁河北塔吊租赁
西安塔吊租赁塔吊租赁/
Adding Fractions with different
denominators
Problem:
You can’t add fractions with different denominators without getting them ready first. They will be ready to add when they have common denominators
Solution:
Turn fractions into equivalent fractions with a common denominator that is find the Lowest Common Multiple (LCM) of the two denominators
Lowest Common Denominator •The lowest common multiple of two numbers is the lowest number in BOTH lists of multiples 3121 Multiples of 2 are 2, 4, 6, 8, 10……Multiples of 3 are 3, 6, 9, 12, ………What is the lowest common multiple?
Lowest Common Denominator •The lowest common multiple of two numbers is the lowest number they will BOTH divide into 3121 2 divides into 2, 4, 6, 8…..3 divides into 3, 6, 9….
What is the lowest number 2 and 3 both divide into?
+
The Lowest Common Multiple of 2 and 3 is 6 so turn all fractions into sixths 6
5626322313321=+=⨯+
⨯You can’t add fractions with
different denominators Special form of 1
3121+
10
9
104105
=
+5
221
+Lowest common denominator is 10 so make all fractions tenths
4
131+
Turn both fractions into twelfths
12
7
123124=
+
3273+What is the lowest number BOTH 3 and 7 divide into?Hmmmmm??????It is 21. So that is my common denominator
21?21?+=What special form of 1 will change 7 to 21. Hmmmm?It is 3/3So I multiply 3/7 by 3/3⨯33What special form of 1 will change 3 to 21. Hmmmm?It is 7/7So I multiply 2/3 by 7/777⨯Now 3x3=9 and 2x7=14Now I know the new numerators
2114219+=Finally the fractions are READY to add. I just have to add the numerators 9+14=2321
212123==
Adding Mixed Numbers •Separate the fraction and the whole number sections, add them separately and recombine at the end 2++
+++2131565
7==
=765
2+21315。