12+1+10+30+20 bằng mấy ?
20+20+30+30+10+10+1+1 bằng mấy ?
20+20+30+30+10+10+1+1
=20.2+30.2+10.2+1.2
=40+60+20+2
=100+20+2
=120+2
=122
9/10- 1/90 - 1/72 - 1/56 - 1/30 - 1/20 - 1/12 - 1/6 -1/2
tinh bằng cách thuận tiện nhất
\(\frac{9}{10}-\frac{1}{90}-\frac{1}{72}-...-\frac{1}{6}-\frac{1}{2}\)
\(=\frac{9}{10}-\left(\frac{1}{2}+\frac{1}{6}+...+\frac{1}{72}+\frac{1}{90}\right)\)
\(=\frac{9}{10}-\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(=\frac{9}{10}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)
\(=\frac{9}{10}-\left(1-\frac{1}{10}\right)\)
\(=\frac{9}{10}-\frac{9}{10}=0\)
Đúng ghi (Đ),Sai ghi (S)
A . 15 phút bằng 15/10 giờ D . 50 phút bằng 1/2 giờ
B . 20 phút bằng 1/3 giờ E . 45 phút bằng 3/4 giờ
C . 30 phút bằng 1/2 giờ F . 10 phút bằng 1/12 giờ
\(A.S\\ B.Đ\\ C.Đ\\ D.S\\ E.Đ\\ F.S\)
Tập hợp ước số của số 60 là:
A. Ư(60) = {1; 2; 3; 5; 12; 20; 30; 60}
B. Ư(60) = {1; 2; 3; 4; 15; 20; 30; 60}
C. Ư(60) = {1; 2; 3; 4; 5; 12; 15; 20; 30; 60}
D. Ư(60) = {1; 2; 3; 4; 5; 6; 10; 12 15; 20; 30; 60}
30-20 cộng 30-14 cộng 20 -10 cộng 46-12 -1 cộng34
30-20+30-14+20-10+46-12-1+34
=(30-20)+(30-14)+(20-10)+(46-12-1)+34
=10+16+10+33+34
=26+10+33+34
=36+33+34
=69+34
=103
Nêu có ngoặc thì bằng 103
Nếu ko ngoặc thì bằng 143
Tìm các phân số bằng nhau trong các phân số: 20/35; 2/3; 5/15; 12/21; 8/10; 20/30; 4/7
\(\dfrac{20}{35}\text{=}\dfrac{4}{7}\)
\(\dfrac{5}{15}\text{=}\dfrac{1}{3}\)
\(\dfrac{12}{21}\text{=}\dfrac{4}{7}\)
\(\dfrac{8}{10}\text{=}\dfrac{4}{5}\)
\(\dfrac{20}{30}\text{=}\dfrac{2}{3}\)
\(\Rightarrow\left(\dfrac{20}{35}\text{=}\dfrac{12}{21}\text{=}\dfrac{4}{7}\right);\left(\dfrac{20}{30}\text{=}\dfrac{2}{3}\right).\)
-10/3 + 13/10-1/6+7/10
1-20/6 +39/30-4/24+34/50
15/24-6/26+28/48-30/39+10/24
-5/10+12/28-3/27-7/18+20/35
\(M=\frac{\text{2 . 6 . 10 + 4 . 12 . 20 + 6 . 18 . 30 + ..... + 20 . 60 . 100}}{\text{1 . 2 . 3 + 2 . 4 . 6 + 3 . 6 . 9 + ..... + 10 . 20 . 30}}\)
Rút gọn biểu thức trên nha.
\(M=\frac{2.6.10+4.12.20+...+20.60.100}{1.2.3+2.4.6+...+10.20.30}=\frac{2.6.10.1^3+2.6.10.2^3+...+2.6.10.10^3}{1.2.3.1^3+1.2.3.2^3+...+1.2.3.10^3}\)
\(=\frac{2.6.10.\left(1^3+2^3+...+10^3\right)}{1.2.3.\left(1^3+2^3+...+10^3\right)}=\frac{2.6.10}{1.2.3}=20\)
vậy M=20
Tính nhanh :
1/2 + 2/4 + 3/6 + 4/8 + 5/10 + 6/12 =
1/3 + 1/4 + 1/5 + 8/10 + 20/15 + 20/30 =
`1/2+2/4+3/6+4/8+5/10+6/12`
`=1/2+1/2+1/2+1/2+1/2+1/2`
`=1/2*6=3`
`1/3+1/4+1/5+8/10+20/15+20/30`
`=(1/3+1/4)+(1/5+4/5)+(4/3+2/3)`
`=7/12+1+2`
`=7/12+3=43/12`
\(\dfrac{1}{2}+\dfrac{2}{4}+\dfrac{3}{6}+\dfrac{4}{8}+\dfrac{5}{10}+\dfrac{6}{12}\)
\(=\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{1}{2}\)
\(=\dfrac{1}{2}\times6=3\)
\(------\)
\(\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{8}{10}+\dfrac{20}{15}+\dfrac{20}{30}\)
\(=\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{4}{5}+\dfrac{4}{3}+\dfrac{2}{3}\)
\(=\left(\dfrac{1}{3}+\dfrac{4}{3}+\dfrac{2}{3}\right)+\left(\dfrac{1}{5}+\dfrac{4}{5}\right)+\dfrac{1}{4}\)
\(=\dfrac{7}{3}+1+\dfrac{1}{4}\)
\(=\dfrac{28}{12}+\dfrac{12}{12}+\dfrac{3}{12}\)
\(=\dfrac{43}{12}\)
`=1/2+1/2+1/2+1/2+1/2+1/2= 1/2 \times 6=3`
`----`
`=1/3+1/4+1/5+4/5+4/3+2/3 =(4/3+2/3+)+(1/5+4/5)+1/3+1/4=2+1+1/3+1/4=3+1/3+1/4=43/12`