Tính
28 + 21 : 7 =
(28 + 21) : 7 =
Tính nhẩm:
35 : 5 =
28 : 7 =
24 : 6 =
21 : 3 =
35 : 7 =
28 : 4 =
24 : 4 =
21 : 7 =
Học sinh nhẩm và ghi kết quả như sau:
35 : 5 = 7
28 : 7 = 4
24 : 6 = 4
21 : 3 = 7
35 : 7 = 5
28 : 4 = 7
24 : 4 = 6
21 : 7 = 3
35 : 5 = 7
28 : 7 = 4
24 : 6 = 4
21 : 3 = 7
35 : 7 = 5
28 : 4 = 7
24 : 4 = 6
21 : 7 = 3
Rút gọn rồi tính:
28/35+21/28+7/21+1/7
28/35+21/28+7/21+1/7
=4/5+3/4+1/3+1/7
=851/420
\(\frac{28}{35}+\frac{21}{28}+\frac{9}{21}+\frac{1}{7}\)
\(=(\frac{4}{5}+\frac{3}{4})+(\frac{3}{7}+\frac{1}{7})\)
\(=\frac{31}{20}+\frac{4}{7}\)
\(=2\frac{17}{140}\)
Chúc bn học tốt!!!!
Viết vào chỗ chấm :
7 x 3 = ... 7 x 6 = ... 7 x 5 = ... 7 x 4 = ...
21 : 7 = ... 42 : 7 = ... 35 : 7 = ... 28 : 7 = ...
21 : 3 = ... 42 : 6 = ... 35 : 5 = ... 28 : 4 = ...
7 x 3 = 21 7 x 6 = 42 7 x 5 = 35 7 x 4 = 28
21 : 7 = 3 42 : 7 = 6 35 : 7 = 5 28 : 7 = 4
21 : 3 = 7 42 : 6 = 7 35 : 5 = 7 28 : 4 = 7
7 × 3 = 21 7 × 6 = 42 7 × 5 = 35. 7 × 4 = 28
21 : 7 = 3. 42 : 7 = 6. 35 : 7 = 5. 28 : 7 = 4
21 : 3 = 7. 42 : 6 = 7. 35 : 5 = 7. 28 : 4 = 7
Tính theo mẫu :
Mẫu : 13/21 + 5/7 = 13/21 + 5 x 3 / 7 x 3 = 13/21 + 15/21 = 28/21
26/81 + 4/27
5/64 + 7/8
\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26+12}{81}=\dfrac{38}{81}\)
\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5+56}{64}=\dfrac{61}{64}\)
\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26}{81}+\dfrac{4\times3}{27\times3}=\dfrac{26}{81}+\dfrac{12}{81}=\dfrac{38}{81}\)
\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5}{64}+\dfrac{7\times8}{8\times8}=\dfrac{5}{64}+\dfrac{56}{64}=\dfrac{61}{64}\)
7 x 2 = ..... 7 x 4 = ..... 7 x 6 = ..... 7 x 3 = .....
2 x 7 = ..... 4 x 7 = ..... 6 x 7 = ..... 3 x 7 = .....
14 : 7 = ..... 28 : 7 = ..... 42 : 7 = ..... 21 : 7 = .....
14 : 2 = ..... 28 : 4 = ..... 42 : 6 = ..... 21 : 3 = .....
7 x 2 = 14 7 x 4 = 28 7 x 6 = 42 7 x 3 = 21
2 x 7 = 14 4 x 7 = 28 6 x 7 = 42 3 x 7 = 21
14 : 7 = 2 28 : 7 = 4 42 : 7 = 6 21 : 7 = 3
14 : 2 = 7 28 : 4 = 7 42 : 6 = 7 21 : 3 = 7
Phân số nào dưới đây bằng phân số 7/3 ? A. 21/15 B. 28/21 C. 21/12 D. 28/12
28/23+19/21-5/23+7/10+2/21
\(\frac{28}{23}+\frac{19}{21}-\frac{5}{23}+\frac{7}{10}+\frac{2}{21}\)
\(=\left(\frac{28}{23}-\frac{5}{23}\right)+\left(\frac{19}{21}+\frac{2}{21}\right)+\frac{7}{10}\)
\(=\frac{23}{23}+\frac{21}{21}+\frac{7}{10}\)
\(=1+1+\frac{7}{10}=2\frac{7}{10}=2,7\)
28/23+19/21-5/23+7/10+2/21=(28/23-5/23)+(19/21+2/21)+7/10=23/23+21/21+7/10=1+1+7/10=2+7/10=27/10
a) 7/-25+8/25 ; 4/5+4/-18 ; 7/21+9/-36
b) 12/20-2/5 ; 2/3-(-5/6) ; 6-3/20
c)2/21*(-7/3) ; 27/28*(-21) ; -15/7*(-14/25)
a) \(\dfrac{7}{-25}+\dfrac{8}{25}=\dfrac{-7}{25}+\dfrac{8}{25}=\dfrac{1}{25}\)
\(\dfrac{4}{5}+\dfrac{4}{-18}=\dfrac{4}{5+\left(-18\right)}=\dfrac{4}{-13}=\dfrac{-4}{13}\)
\(\dfrac{7}{21}+\dfrac{9}{-36}=\dfrac{1}{3}+\dfrac{1}{-4}=\dfrac{1}{3+\left(-4\right)}=\dfrac{1}{-1}=1\)
b) \(\dfrac{12}{20}-\dfrac{2}{5}=\dfrac{12}{20}+\left(\dfrac{-2}{5}\right)=\dfrac{3}{5}+\dfrac{-2}{5}=\dfrac{3+\left(-2\right)}{5}=\dfrac{1}{5}\)
\(\dfrac{2}{3}-\dfrac{-5}{6}=\dfrac{2}{3}+\dfrac{5}{6}=\dfrac{4}{6}+\dfrac{5}{6}=\dfrac{9}{6}=\dfrac{3}{2}\)
\(6-\dfrac{3}{20}=6+\dfrac{-3}{20}=\dfrac{60}{60}+\dfrac{-9}{60}=\dfrac{51}{60}\)
c) \(\dfrac{2}{21}.\dfrac{-7}{3}=\dfrac{2.\left(-1\right)}{7.3}=\dfrac{-2}{21}\)
\(\dfrac{27}{28}.\left(-21\right)=\dfrac{27.\left(-21\right)}{28}=\dfrac{-567}{28}\)
\(\dfrac{-15}{7}.\dfrac{-14}{25}=\dfrac{-3.\left(-2\right)}{1.5}=\dfrac{6}{5}\)
A=21/28-54/72:(21/28+48/72)
B=8/11.7/19+-12/19+7/19.-3/11