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)    \(\frac{1}{8}+\frac{1}{12}+\frac{3}{8}+\frac{5}{12}\)

\(=\left(\frac{1}{8}+\frac{3}{8}\right)+\left(\frac{1}{12}+\frac{5}{12}\right)\)

\(=\frac{1}{2}+\frac{1}{2}=1\)

1. = 1+2+3/7 = 6/7

2. = (3/7+4/7) + (4/9+5/9) = 1+1 = 2

Tk mk nha

\(\frac{1}{7}+\frac{2}{7}+\frac{3}{7}=\frac{1+2+3}{7}=\frac{6}{7}\)

\(\frac{3}{7}+\frac{4}{9}+\frac{4}{7}+\frac{5}{9}\)

\(=\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{4}{9}+\frac{5}{9}\right)\)

\(=1+1\)

\(=2\)

1) \(\frac{1}{7}+\frac{2}{7}+\frac{3}{7}=\frac{6}{7}\)

2) \(\frac{3}{7}+\frac{4}{9}+\frac{4}{7}+\frac{5}{9}\)

\(=\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{5}{9}+\frac{4}{9}\right)\)

\(=\frac{7}{7}+\frac{9}{9}\)

\(=1+1=2\)

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

A = (2 + 2²) + (2³ + 2⁴ ) +…(2¹⁹⁹ + 2²⁰⁰)

A = 6 + 2² (2 + 2² ) +… + 2¹⁹⁸ (2 + 2²)

A = 6 + 2² (6 ) +… + 2¹⁹⁸ (6)

A = 6(1 + 2² +… + 2¹⁹⁸)

Vậy A chia hết cho 6

a) \(\left(\frac{2}{7}+\frac{3}{8}+\frac{12}{7}+\frac{5}{8}\right).\frac{19}{36}\)

\(=\left\{\left(\frac{2}{7}+\frac{12}{7}\right)+\left(\frac{3}{8}+\frac{5}{8}\right)\right\}.\frac{19}{36}\)

\(=\left(\frac{14}{7}+\frac{8}{8}\right).\frac{19}{36}\)

\(=\left(2+1\right).\frac{19}{36}\)

\(3.\frac{19}{36}=\frac{19}{12}\)

a.\(\dfrac{18}{15}+\dfrac{7}{15}+\dfrac{12}{15}=\dfrac{18+7+12}{15}=\dfrac{37}{15}\)

b.\(\dfrac{9}{7}+\dfrac{8}{7}+\dfrac{11}{7}=\dfrac{9+8+11}{7}=\dfrac{28}{7}=4\)

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

= ( 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 

Ta có : \(1+2+3+...+19+20\)

          \(=\frac{\left(20+1\right).20}{2}=\frac{21.20}{2}=210\)

a) 18/15 + 7/15 + 12/15 =18/15 + 12/15 + 7/15        

                                    = 30/15 + 7/15

                                     =       37/15

b) 9/7 + 8/7 +11/7 = 9/7 + 11/7 + 8/7 

                         =  20/7  + 8/7 =  28/7 nha . tk mk nhé b

a, 18/15+7/15+12/15= 37/15

b, 9/7+8/7+11/7=28/7=4

a ) \(\frac{18}{15}\)+ \(\frac{7}{15}\)+ \(\frac{12}{15}\)= \(\frac{37}{15}\)

b )\(\frac{9}{7}\)+ \(\frac{8}{7}\)+ \(\frac{11}{7}\)= 4

(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+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

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

= 10 . 10 +10 

=  100     +  10 = 110

a) \(\frac{18}{15}+\frac{7}{15}+\frac{12}{15}\)

= \(\frac{18+7+12}{15}\)

= \(\frac{37}{15}\)

b) \(\frac{9}{7}+\frac{8}{7}+\frac{11}{7}\)

= \(\frac{9+8+11}{7}\)

= \(\frac{28}{7}\)

a) 18/15 + 7/15 + 12/15

= (18/15 + 12/15) + 7/15

= 30/15 + 7/15

= 37/15

b) 9/7 + 8/7 + 11/7

= (9/7 + 11/7) + 8/7

= 20/7 + 8/7

= 28/7

chuc ban hok tot

a)18/15+7/15+12/15=(18/15+12/15)+7/15=30/15+7/15=37/15

b)9/7+8/7+11/7=(9/7+11/7)+8/7=20/7+8/7=28/7=4

đúng thì k cho mik nha