Dividing fractions
- 2. SIMPLE DIVISION 10 2=5 How else can we divide 10 by 2?
- 3. 10 ÷ 2 = 5 How else can we divide 10 by 2? 10 x 1 10 1 10 10 x 2 = 1 x 2 =2= 5 You can multiply by the reciprocal of 2 and you will get the same result. 1 2 and are called multiplicative 2 inverses, or reciprocals.
- 4. METHOD #1: USING THE RULES FOR DIVIDING FRACTIONS: “K. C. F.” 1) Keepthe first fraction. 2) Change the to x. 3) Flip the second fraction. 1 3 1 Ex: a) 5 4 b) 2 4 3 2 6 1 K C FK C Fx= = 1 4 1 2 4 5 x 4 = 20
- 5. METHOD #2: MODELING How can the quotient be larger than the dividend and/or divisor? 1 5 4 This actually means how many ¼-sized pieces can fit into 5 wholes?
- 6. MORE MODELING… 3 1 4 2 How many ½-sized pieces fit in ¾? 3 4 1 1 2 2 1 whole and 1 half of the ½-sized pieces fit in the ¾ space, so = 3 1 1 1 4 2 2
- 7. EVEN MORE MODELING… 1 3 2 ÷ 4 What part of the ¾-sized piece fits in ½? 1 2 3 4 2 of the ¾-sized 3 piece fits in ½
- 8. METHOD #3: DIVIDING DECIMALS INSTEAD Students can turn both fractions into decimals and can divide those instead: 1 = 0.5 3 = 0.75 2 4 3 1 1 3 ÷ = 0.75 ÷ 0.5 ÷ = 0.5 ÷ 0.75 4 2 2 4