CHƯƠNG 4: PHÂN SỐ - CÁC PHÉP TÍNH VỚI PHÂN SỐ. GIỚI THIỆU HÌNH THOI

2016/1

\(\dfrac{2}{9}+\dfrac{3}{7}+\dfrac{15}{13}+\dfrac{4}{7}-\dfrac{2}{13}+\dfrac{7}{9}\)

\(=\left(\dfrac{2}{9}+\dfrac{7}{9}\right)+\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\left(\dfrac{15}{13}-\dfrac{2}{13}\right)\)

\(=\dfrac{9}{9}+\dfrac{7}{7}+\dfrac{13}{13}=1+1+1=3\)

`2/9+3/7+15/13+4/7-2/13+7/9`

`= (2/9 + 7/9 ) + ( 3/7 + 4/7 ) + ( 15/13-2/13 ) `

`= 9/9 + 7/7 + 13/13`

`=   1 + 1 + 1 = 3`

`3/4 xx4/5 +3/4xx8/5-3/4xx7/5`

`=3/4xx(4/5+8/5-7/5)`

`=3/4xx5/5`

`=3/4xx1`

`=3/4`

ღYêᑌ_ ᒪღ

`3/4 xx 4/5 + 3/4 xx 8/5 - 3/4 xx 7/5`

`=3/4 xx (4/5 + 8/5 -7/5)`

`= 3/4 xx 5/5`

`= 3/4 xx 1`

`= 3/4`

\(a,\dfrac{12}{15}+\dfrac{13}{15}\\ =\dfrac{12+13}{15}\\ =\dfrac{25}{15}\\ =\dfrac{5}{3}\\ b,\dfrac{25}{35}-\dfrac{18}{35}\\ =\dfrac{25-18}{35}\\ =\dfrac{7}{35}=\dfrac{1}{5}\\ c,\dfrac{9}{5}+\dfrac{3}{4}=\dfrac{36}{20}+\dfrac{15}{20}\\ =\dfrac{36+15}{20}\\ =\dfrac{51}{20}\\ d,\dfrac{18}{12}-\dfrac{8}{6}\\ =\dfrac{18}{12}-\dfrac{16}{12}\\ =\dfrac{2}{12}\\ =\dfrac{1}{6}\\ đ,3+\dfrac{2}{3}\\ =\dfrac{3}{1}+\dfrac{2}{3}\\ =\dfrac{9}{3}+\dfrac{2}{3}\\ =\dfrac{11}{3}\\ e,3-\dfrac{1}{3}\\ =\dfrac{3}{1}-\dfrac{1}{3}\\ =\dfrac{9}{3}-\dfrac{1}{3}\\ =\dfrac{8}{3}\\ i,\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}\\ =\dfrac{6}{12}+\dfrac{4}{12}+\dfrac{3}{12}\\ =\dfrac{13}{12}\\ g,\dfrac{9}{2}-\dfrac{1}{3}-\dfrac{2}{4}\\ =\dfrac{54}{12}-\dfrac{4}{12}-\dfrac{6}{12}\\ =\dfrac{44}{12}\\ =\dfrac{11}{3}\)

Bài 4:

Mẫu là (120+20)/2=140/2=70

Tử là 70-20=50

`6/15 + 5/15 = (6+5)/15= 11/15`

`4/8 + 3/5= 20/40 + 24/40= 44/40=11/10`

`1/2 + 5/10= 5/10 + 5/10=10/10=1`

`1/2+1/3+1/4= 6/12 + 4/12 + 3/12=13/12`

`a) 6/15 + 5/15 = 11/15 `

`b) 4/8 + 3/5 = 20/40 + 24/40 = 44/40 = 11/10 `

`c) 1/2 + 5/10 = 5/10 + 5/10 =  10/10 = 1 `

`d) 1/2 + 1/3 + 1/4 = 6/12 + 4/12 + 3/12 = 13/12 `

  học tốt

Trong tháng 1 phải trả:

360000*1/4=90000 đồng

Trong tháng 2 phải trả:

360000*1/3=120000 đồng

`160/320=(160:10)/(320:10)=16/32=(16:2)/(32:2)=8/16=(8:2)/(16:2)=4/8=1/2`

Bài 2:
\(\dfrac{160}{320}=\dfrac{16}{x}=\dfrac{y}{16}=\dfrac{4}{z}=\dfrac{1}{2}\)
\(x=\dfrac{16\times320}{160}=32\)
\(y=\dfrac{16\times16}{32}=8\)
\(z=\dfrac{4\times2}{1}=8\)

\(\dfrac{21}{36}=\dfrac{21:3}{36:3}=\dfrac{7}{12}\)

\(\dfrac{21}{36}=\dfrac{21:3}{36:3}=\dfrac{7}{12}\)

`26/54=(26:2)/(54:2)=13/27`

\(\dfrac{26}{54}=\dfrac{26:2}{54:2}=\dfrac{13}{27}\)

Rút gọn phân số12 Phần 26

Phân số thỏa mãn yêu cầu: \(\dfrac{2}{15}\)

là 2/15 nha