- Tinh tổng : a.1/3 + 1/16 + 1/18 . b. 1/12 + 1/16 +3/4
- Tinh bằng cách thuận tiện nhất a. 1/15+4/15+5/18+7/18 b. 1/8 + 1/12 + 3/8 + 5/12 .
K
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Những câu hỏi liên quan
KT
7 tháng 2 2018
1) \(\frac{1}{12}+\frac{1}{16}+\frac{3}{4}\)
\(=\frac{4}{48}+\frac{3}{48}+\frac{36}{48}\)
\(=\frac{4+3+36}{48}\)
\(=\frac{43}{48}\)
2) a) \(\frac{1}{15}+\frac{4}{15}+\frac{5}{18}+\frac{7}{18}\)
\(=\left(\frac{1}{15}+\frac{4}{15}\right)+\left(\frac{5}{18}+\frac{7}{18}\right)\)
\(=\frac{1}{3}+\frac{2}{3}=1\)
b) \(\frac{1}{8}+\frac{1}{12}+\frac{3}{8}+\frac{5}{12}\)
\(=\left(\frac{1}{8}+\frac{3}{8}\right)+\left(\frac{1}{12}+\frac{5}{12}\right)\)
\(=\frac{1}{2}+\frac{1}{2}=1\)
LH
2
26 tháng 2 2018
a ) \(\frac{1}{15}+\frac{4}{15}+\frac{5}{18}+\frac{7}{18}\)
\(=\left(\frac{1}{15}+\frac{4}{15}\right)+\left(\frac{5}{18}+\frac{7}{18}\right)\)
\(=\frac{1}{3}+\frac{2}{3}\)
\(=1\)
b ) \(\frac{1}{8}+\frac{1}{12}+\frac{3}{8}+\frac{5}{12}\)
\(=\left(\frac{1}{8}+\frac{3}{8}\right)+\left(\frac{1}{12}+\frac{5}{12}\right)\)
\(=\frac{1}{2}+\frac{1}{2}\)
\(=1\)
26 tháng 2 2018
a, \(\frac{1}{15}\)+ \(\frac{4}{15}\)+ \(\frac{5}{18}\)+ \(\frac{7}{18}\)= ( \(\frac{1}{15}\)+ \(\frac{4}{15}\)) + ( \(\frac{5}{18}\)+ \(\frac{7}{18}\))
= \(\frac{1}{3}\)+ \(\frac{2}{3}\)
= \(\frac{3}{3}\)= 1
b,\(\frac{1}{8}\)+ \(\frac{1}{12}\)+ \(\frac{3}{8}\)+ \(\frac{5}{12}\)= ( \(\frac{1}{8}\)+ \(\frac{3}{8}\)) + ( \(\frac{1}{12}\)+ \(\frac{5}{12}\))
= \(\frac{1}{2}\)+ \(\frac{1}{2}\)
= \(\frac{2}{2}\)= 1
MG
28 tháng 4 2018
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+20+10
=20+20+20+20+20+20+20+20+20+20+10
=20×10+10
=200+10
=210
28 tháng 4 2018
= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) + (4 + 16 ) + ( 5 + 15 ) + ( 6 + 14 ) + ( 7 + 13 ) + ( 8 + 12) + ( 9+ 11 ) + 20
= 20 + 20 + 20 +20 + 20 +20 + 20 + 20 + 20 +20
= 20 x 10
= 200
tui đầu tiên đó
22 tháng 3 2022
A) 3/7 + 4/9 + 4/7 + 5/9 = ( 4/9+5/9) + ( 3/7 + 4/7) = 1+ 1 = 2
B) 1/5 + 4/11 + 4/5 + 7/11 = ( 4/11 + 7/11) + ( 1/5 + 4/5) = 1+1=2
C) 1/15 + 4/15 + 5/18 + 7/18= ( 1/15+4/15) + (5/18+7/15)= 5/15 + 12/15 = 17/15
D) 1/8 + 1/12 + 3/8 + 5/12 = (1/8 + 3/8) + ( 1/12 + 1/12) = 4/8 + 2/12 = 64/96
K nha
LB
1 tháng 12 2017
(19+1)+(18+2)+(17+3)+(16+4)+(15+5)+(14+6)+(13+7)+(12+8)+(11+9)+20)+10
=20+20+20+20+20+20+20+20+20+20=(20*10)+10
=210
1 tháng 12 2017
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+(10+20)
=20+20+20+20+20+20+20+20+20+30
=(20 x 9) + 30
=180 + 30
=210
tk nha
24 tháng 2 2019
a,17/23 + (1 - 17/23)
= 17/23 + 6/23
= 23/23 = 1
b,17/12 + 9/7 - (2/7 + 5 /12)
= (17/12 - 5/12) + (9/7 + 2/7)
= 1+1 = 2
c, 7/13 - ( 4/7 -6/13 )
= 7/13 - 4/7+ 6/13
= (7/13 + 6/13) -4/7
= 13/13 -4/7
= 1 -4/7 = 3/7
hok tốt✍️ ✍️
BD
24 tháng 2 2019
a) 17/23+(1-17/23)
=17/23+1-17/23
=1
b)17/12+9/7-(2/7+5/12)
=17/12+9/7-2/7-5/12
=1+1
=2
c)
7/13-(4/7-6/13)
=7/13-4/7+6/13
=1-4/7
=3/7
KK
24 tháng 2 2019
a) 17/23 + (1 - 17/23)
= 17/23 + 1 - 17/23
= (17/23 - 17/23) + 1
= 0 + 1 = 1
b) 17/12 + 9/7 - (2/7 + 5/12)
= 17/12 + 9/7 - 2/7 - 5/12
= (17/12 - 5/12) + (9/7 - 2/7)
= 1 + 1 = 2
c) 7/13 - (4/7 - 6/13)
= 7/13 - 4/7 + 6/13
= (6/13 + 6/12) - 4/7
= 1 - 4/7 = 3/7
d) 7/18 + 3/16 + 11/18 + 13/16
= (7/18 + 11/18) + (3/16 + 13/16)
= 1 + 1 = 1
KK
24 tháng 2 2019
d) sửa 7/18 + 3/16 + 11/18 + 13/16
= (7/18 + 11/18) + (3/16 + 13/16)
= 1 + 1
= 2
26 tháng 10 2019
c) \(\left(11+12+13+...+19\right).\left(6.8-48\right)=\left(11+12+13+...+19\right).\left(48-48\right)\)
\(=\left(11+12+13+...+19\right).0\)
\(=0\)
Hok "tuốt" nha^^
26 tháng 10 2019
b) \(\left(500.9-250.18\right).\left(1+2+3+...+9\right)=\left(250.2.9-250.18\right).\left(1+2+...+9\right)\)
\(=\left(250.18-250.18\right).\left(1+2+3+...+9\right)\)
\(=0.\left(1+2+3+...+9\right)\)
\(=0\)
Hok tốt nha^^ (lần 2)
1. = 1+2+3/7 = 6/7
2. = (3/7+4/7) + (4/9+5/9) = 1+1 = 2
Tk mk nha
\(\frac{1}{7}+\frac{2}{7}+\frac{3}{7}=\frac{1+2+3}{7}=\frac{6}{7}\)
\(\frac{3}{7}+\frac{4}{9}+\frac{4}{7}+\frac{5}{9}\)
\(=\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{4}{9}+\frac{5}{9}\right)\)
\(=1+1\)
\(=2\)