Tính 21 8 - 3 8
tính nhanh
1/7 x 21/8 - 3/8 x 1/7 -1/7 x 2/8
\(\dfrac{1}{7}\times\dfrac{21}{8}-\dfrac{3}{8}\times\dfrac{1}{7}-\dfrac{1}{7}\times\dfrac{2}{8}\\ =\dfrac{1}{7}\times\left(\dfrac{21}{8}-\dfrac{3}{8}-\dfrac{2}{8}\right)\\ =\dfrac{1}{7}\times\dfrac{16}{8}\\ =\dfrac{1}{7}\times2\\ =\dfrac{2}{7}\)
\(\dfrac{1}{7}\times\dfrac{21}{8}-\dfrac{3}{8}\times\dfrac{1}{7}-\dfrac{1}{7}\times\dfrac{2}{8}\)
=\(\dfrac{1}{7}\times\left(\dfrac{21}{8}-\dfrac{3}{8}-\dfrac{2}{8}\right)\)
=\(\dfrac{1}{7}\times2\)
=\(\dfrac{2}{7}\)
\(=\dfrac{1}{7}\text{×}\left(\dfrac{21}{8}-\dfrac{3}{8}-\dfrac{2}{8}\right)\)
\(=\dfrac{1}{7}\text{×}2\)
\(=\dfrac{2}{7}\)
tính
1/3+5/4 4/12-1/15 2/3x15/8 2/3:8/21
`1/3 + 5/4`
`= 4/12 + 15/12`
`= 19/12
__
`4/12 - 1/15`
`= 1/3 -1/15`
`= 5/15 -1/15`
`=4/15`
__
`2/3 xx 15/8`
`= (2xx15)/(3xx88)`
`= 30/24`
`=5/4`
__
`2/3 : 8/21`
`= 2/3 xx 21/8`
`= (2xx21)/(3xx8)`
`= 42/24`
`=7/4`
1/3+5/4=4/12+15/12
=19/12
4/12-1/15=20/60-4/60
=16/60=4/15
2/3x15/8=30/24=5/4
2/3:8/21=42/24=7/4
nhớ cho a tích nhé =)) a bị bịp nhiều rồi
\(\dfrac{1}{3}+\dfrac{5}{4}=\dfrac{4}{12}+\dfrac{15}{12}=\dfrac{19}{12}\)
_____________________________\(\dfrac{4}{12}-\dfrac{1}{15}=\dfrac{60}{180}-\dfrac{12}{180}=\dfrac{48}{180}=\dfrac{4}{15}\)
_____________________________
\(\dfrac{2}{3}\)x\(\dfrac{15}{8}\)\(=\dfrac{30}{24}=\dfrac{5}{4}\)
_____________________________
\(\dfrac{2}{3}:\dfrac{8}{21}=\dfrac{2}{3}\)x\(\dfrac{21}{8}=\)\(\dfrac{42}{24}=\dfrac{7}{4}\)
Chúc bạn học tốt:>
Tính nhanh
\(\frac{5}{11}+3\frac{8}{21}+\frac{6}{11}-\frac{8}{21}\)
\(\frac{5}{11}+3\frac{8}{21}+\frac{6}{11}-\frac{8}{21}\)
\(=\frac{5}{11}+\frac{71}{21}+\frac{6}{11}-\frac{8}{21}\)
\(=\left(\frac{5}{11}+\frac{6}{11}\right)+\left(\frac{71}{21}-\frac{8}{21}\right)\)
\(=1+3\)
\(=4\)
Đúng lun, Mn tk mk nha!
\(\frac{5}{11}+3\frac{8}{21}+\frac{6}{11}-\frac{8}{21}\)
=\(\frac{5}{11}+\frac{71}{21}+\frac{6}{11}-\frac{8}{21}\)
=\(\left(\frac{5}{11}+\frac{6}{11}\right)+\left(\frac{71}{21}-\frac{8}{21}\right)\)
=\(1+3\)
=
mik quên chưa ghi đáp án, xin lỗi nha
\(\frac{5}{11}+3\frac{8}{21}+\frac{6}{11}-\frac{8}{21}\)
=\(\frac{5}{11}+\frac{71}{21}+\frac{6}{11}-\frac{8}{21}\)
=\(\left(\frac{5}{11}+\frac{6}{11}\right)+\left(\frac{71}{21}-\frac{8}{21}\right)\)
=\(1+3\)
=\(4\)
tính nhanh :
a, 3 - 6 + 9 - 12 + 15 - 18 + 21
b, 48 : 8 + 24 : 8 + 8 : 8
a, 3 - 6 + 9 - 12 + 15 - 18 + 21
= 3 + 9 + 15 + 21 -6 -12- 18
=(21 - 18) + (15 - 12) + (9 - 6) +3
= 3 + 3 + 3 + 3
=3 *4
= 12
b,, 48 :8 + 24 : 8 + 8 : 8
= (48 + 24 + 8) : 8
= 80 : 8
= 10
k cho mình nha ....
a, 3 - 6 + 9 - 12 + 15 - 18 + 21 = 12
b, 48 : 8 + 24 : 8 + 8 : 8 = 10
Tính nhanh:
a) A= 38.78-(214-1)(214+1)
Tính rồi rút gọn.
a) \(\dfrac{3}{8}:\dfrac{9}{4}\) b) \(\dfrac{8}{21}:\dfrac{4}{7}\) c) \(\dfrac{5}{8}:\dfrac{15}{8}\)
a) \(\dfrac{3}{8}:\dfrac{9}{4}\)
\(=\dfrac{3}{8}\times\dfrac{4}{9}\)
\(=\dfrac{3\times4}{8\times9}\)
\(=\dfrac{1\times1}{2\times3}\)
\(=\dfrac{1}{6}\)
b) \(\dfrac{8}{21}:\dfrac{4}{7}\)
\(=\dfrac{8}{21}\times\dfrac{7}{4}\)
\(=\dfrac{8\times7}{21\times4}\)
\(=\dfrac{2\times1}{3\times1}\)
\(=\dfrac{2}{3}\)
c) \(\dfrac{5}{8}:\dfrac{15}{8}\)
\(=\dfrac{5}{8}\times\dfrac{8}{15}\)
\(=\dfrac{5\times8}{8\times15}\)
\(=\dfrac{1\times1}{1\times3}\)
\(=\dfrac{1}{3}\)
a: \(=\dfrac{3}{8}\cdot\dfrac{4}{9}=\dfrac{12}{72}=\dfrac{1}{6}\)
b: \(=\dfrac{8}{21}\cdot\dfrac{7}{4}=\dfrac{56}{84}=\dfrac{2}{3}\)
c: \(=\dfrac{5}{8}\cdot\dfrac{8}{15}=\dfrac{5}{15}=\dfrac{1}{3}\)
Tính nhẩm:
2 × 8 = ... | 16 : 2 = ... |
21 : 3 = ... | 4 × 5 = ... |
3 × 8 = ... | 24 : 3 = ... |
5 × 6 = ... | 5 × 4 = ... |
4 × 8 = ... | 40 : 4 = ... |
28 : 4 = ... | 20 : 4 = ... |
5 × 8 = ... | 40 : 5 = ... |
3 × 6 = ... | 20 : 5 = ... |
Phương pháp giải:
Nhẩm bảng nhân, chia trong phạm vi đã học rồi điền kết quả vào chỗ trống.
Lời giải chi tiết:
2 × 8 = 16 | 16 : 2 = 8 |
21 : 3 = 7 | 4 × 5 = 20 |
3 × 8 = 24 | 24 : 3 = 8 |
5 × 6 = 30 | 5 × 4 = 20 |
4 × 8 = 32 | 40 : 4 = 10 |
28 : 4 = 7 | 20 : 4 = 5 |
5 × 8 = 40 | 40 : 5 = 8 |
3 × 6 = 18 | 20 : 5 = 4 |
2x8=16
21:3=7
16:2=8
4x5=20
học tốt
2 × 8 = 16 | 16 : 2 = 8 |
21 : 3 = 7 | 4 × 5 = 20 |
3 × 8 = 24 | 24 : 3 = 8 |
5 × 6 =30 | 5 × 4 = 20 |
4 × 8 = 32 | 40 : 4 = 10 |
28 : 4 = 7 | 20 : 4 = 5 |
5 × 8 = 40 | 40 : 5 =8 |
3 × 6 =18 | 20 : 5 = 4 |
Đặt tính rồi tính.
21 437 : 3 36 095 : 8
Tính:
a) (-17).6
b) 8.(-125)
c) (-12).(-15)
d)21.(-3) + (-21).7
1. Tính bằng cách hợp lý
1) 0,625 . 17/13 . 8/3 . -21/51 . (-6)
2) -7/9 . 24/19 + 7/9
3) -3/8 . 7/6 +3/8 . 9/6
1: =5/8*17/13*7/17*8/3*6
=5/3*7/13*6
=5*7*2/13=70/13
2: =-7/9(24/19-1)
=-7/9*5/19
=-35/171
3: =-3/8(7/6-9/6)
=-3/8*(-2/6)
=3/8*1/3=1/8