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2.11 Breuke - vermenigvuldiging van breuke

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Wiskunde

Gewone breuke

Opvoeders afdeling

Memorandum

18.1

OPTELLING

1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {} + 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {} + 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {} + 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {} + 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {}

1 4 size 12{ { { size 8{1} } over { size 8{4} } } } {} + 1 4 size 12{ { { size 8{1} } over { size 8{4} } } } {} + 1 4 size 12{ { { size 8{1} } over { size 8{4} } } } {} + 1 4 size 12{ { { size 8{1} } over { size 8{4} } } } {} + 1 4 size 12{ { { size 8{1} } over { size 8{4} } } } {} + 1 4 size 12{ { { size 8{1} } over { size 8{4} } } } {}

3 7 size 12{ { { size 8{3} } over { size 8{7} } } } {} + 3 7 size 12{ { { size 8{3} } over { size 8{7} } } } {}

2 3 size 12{ { { size 8{2} } over { size 8{3} } } } {} + 2 3 size 12{ { { size 8{2} } over { size 8{3} } } } {} + 2 3 size 12{ { { size 8{2} } over { size 8{3} } } } {}

2 5 size 12{ { { size 8{2} } over { size 8{5} } } } {} + 2 5 size 12{ { { size 8{2} } over { size 8{5} } } } {} + 2 5 size 12{ { { size 8{2} } over { size 8{5} } } } {} + 2 5 size 12{ { { size 8{2} } over { size 8{5} } } } {}

PRODUK

2 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {}

1 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {}

6 7 size 12{ { { size 8{6} } over { size 8{7} } } } {}

2

1 3 5 size 12{ { { size 8{3} } over { size 8{5} } } } {}

b) Getallelyn / Teller x Teller

Noemer x Noemer

d)

(i) 21 10 size 12{ { { size 8{"21"} } over { size 8{"10"} } } } {}

= 2 1 10 size 12{ { { size 8{1} } over { size 8{"10"} } } } {}

(ii) 12 3 size 12{ { { size 8{"12"} } over { size 8{3} } } } {}

= 4

(iii) 84 9 size 12{ { { size 8{"84"} } over { size 8{9} } } } {}

= 9 1 3 size 12{ { { size 8{1} } over { size 8{3} } } } {}

19.1

a) 1

b) 1

c) 1

d) 1

19.2 Produk is elke keer 1

19.4 a) 20 17 size 12{ { { size 8{"20"} } over { size 8{"17"} } } } {}

b) 1 40 size 12{ { { size 8{1} } over { size 8{"40"} } } } {}

c) 5 31 size 12{ { { size 8{5} } over { size 8{"31"} } } } {}

d) 8 73 size 12{ { { size 8{8} } over { size 8{"73"} } } } {}

19.5 c) 5 31 size 12{ { { size 8{5} } over { size 8{"31"} } } } {} : Maak eers onegte breuk ( 31 5 size 12{ { { size 8{"31"} } over { size 8{5} } } } {} )

d) 8 73 size 12{ { { size 8{8} } over { size 8{"73"} } } } {} : Maak eers onegte breuk ( 73 8 size 12{ { { size 8{"73"} } over { size 8{8} } } } {} )

20. a) 1 2 3 size 12{ { { size 8{2} } over { size 8{3} } } } {} x 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {}

= 5 3 size 12{ { { size 8{5} } over { size 8{3} } } } {} x 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {}

= 5 6 size 12{ { { size 8{5} } over { size 8{6} } } } {} m = 83, 3 . size 12{ {3} cSup { size 8{ "." } } } {} cm

b) 5 6 size 12{ { { size 8{5} } over { size 8{6} } } } {} x 1 3 size 12{ { { size 8{1} } over { size 8{3} } } } {} = 5 18 size 12{ { { size 8{5} } over { size 8{"18"} } } } {} m

= 27, 7 . size 12{ {7} cSup { size 8{ "." } } } {} cm

22.

(a) 32

(b) 15

(c) 25

(d) 25

(e) 45

(f) 2

(g) 8

(h) 7

(i) 7

(j) 6

(k) 6

(l) 8

(m) 8

(n) 8

(o) 100

Leerders afdeling

Inhoud

Aktiwiteit: vermenigvuldiging van breuke [lu 1.7.3, lu 2.1.5]

18. VERMENIGVULDIGING VAN BREUKE

18.1 Vermenigvuldiging van breuke met natuurlike getalle

Jy weet reeds dat vermenigvuldiging eintlik herhaalde optelling is.

a) Kyk of jy die volgende tabel kan voltooi:

b) Kyk goed na die voltooide tabel. Kan jy aan ’n korter manier / metode dink om die antwoorde te vind?

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

c) LET OP!

Jy kan ook dié metode volg:

1. Skryf albei getalle as breuke, bv. 6 × 1 4 = 6 1 × 1 4 size 12{6 times { { size 8{1} } over { size 8{4} } } = { { size 8{6} } over { size 8{1} } } times { { size 8{1} } over { size 8{4} } } } {}

2. Vermenigvuldig die tellers met mekaar: 6 × 1 = 6

3. Vermenigvuldig die noemers met mekaar: 1 × 4 = 4

4. Vereenvoudig die antwoord: 6 4 = 1 2 4 = 1 1 2 size 12{ { { size 8{6} } over { size 8{4} } } =1 { { size 8{2} } over { size 8{4} } } =1 { { size 8{1} } over { size 8{2} } } } {}

d) Bereken:

(i) 7 × 3 10 size 12{7 times { { size 8{3} } over { size 8{"10"} } } } {}

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(ii) 2 3 × 6 size 12{ { { size 8{2} } over { size 8{3} } } times 6} {}

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(iii) 12 × 7 9 size 12{"12" times { { size 8{7} } over { size 8{9} } } } {}

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___________________________________________________

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e) Op ’n getallelyn sou ons 6 × 1 4 size 12{6 times { { size 8{1} } over { size 8{4} } } } {} so kon voorstel:

f) Stel die volgende op ’n getallelyn voor: x = 4 × 2 3 size 12{x=4 times { { size 8{2} } over { size 8{3} } } } {}

18.2 Vermenigvuldiging van breuke met breuke

a) Kyk goed na die volgende voorbeelde:

(i) Die helfte ( 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {} ) van ’n driekwart ( 3 4 size 12{ { { size 8{3} } over { size 8{4} } } } {} ) kan so voorgestel word:

Dus: 1 2 × 3 4 = 3 8 size 12{ { { size 8{1} } over { size 8{2} } } times { { size 8{3} } over { size 8{4} } } = { { size 8{3} } over { size 8{8} } } } {}

(ii) Een derde ( 1 3 size 12{ { { size 8{1} } over { size 8{3} } } } {} ) van ’n half ( 1 2 size 12{ { { size 8{1} } over { size 8{2} } } } {} ) lyk so:

Dus 1 3 × 1 2 = 1 6 size 12{ { { size 8{1} } over { size 8{3} } } times { { size 8{1} } over { size 8{2} } } = { { size 8{1} } over { size 8{6} } } } {}

b) Maak nou soortgelyke sketse vir:

(i) 1 5 × 1 2 size 12{ { { size 8{1} } over { size 8{5} } } times { { size 8{1} } over { size 8{2} } } } {}

(ii) 3 10 × 1 2 size 12{ { { size 8{3} } over { size 8{"10"} } } times { { size 8{1} } over { size 8{2} } } } {}

c) LET OP!

As ons ’n breuk met ’n breuk vermenigvuldig, bv. 2 3 × 3 8 size 12{ { { size 8{2} } over { size 8{3} } } times { { size 8{3} } over { size 8{8} } } } {}

1. Vermenigvuldig ons eers die tellers met mekaar: 2 × 3 = 6

2. Dan vermenigvuldig ons die noemers met mekaar: 3 × 8 = 24

3. Ons vereenvoudig ook waar nodig: 6 ÷ 6 24 ÷ 6 = 1 4 size 12{ { { size 8{6~ div ~6} } over { size 8{"24"~ div ~6} } } = { { size 8{1} } over { size 8{4} } } } {}

d) Onthou jy nog?

Om te kan vereenvoudig , moet jy altyd die teller en die noemer deur dieselfde getal deel .

e) Het jy geweet?

Ons kan ook van kansellering gebruik maak om die produk te bepaal.

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Source:  OpenStax, Wiskunde graad 7. OpenStax CNX. Oct 21, 2009 Download for free at http://cnx.org/content/col11076/1.2
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