A=1/2x3+14/4x6+5/20x25+55/30x25

A=1/6+7/12+1/100+11/150

A=(100/600+6/600)+(175/300+22/300)

A=53/300+197/300

A=5/6

Vay A=5/6

a) 145 + 86 + 14 + 55 = ( 145 + 55 ) + (86 + 14 )

= 200 + 100

= 300

b) 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = ( 1+9 +2 + 8) + ( 3 + 7 + 4 + 6 ) + 5

= 20 + 20 + 5

= 45

( 145 + 55) + ( 86 + 14)=
200             +100
300 nhé

145 + 86 + 14 + 55 

=(145+55)+(86+14)

=200+100

=300

145 + 86 + 14 + 55

= ( 145 + 55 ) + ( 86 + 14 )

= 200 + 100

= 300

HT

=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6

=1/2-1/6=1/3

\(\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}=\dfrac{1}{2}-\dfrac{1}{6}=\dfrac{3-1}{6}=\dfrac{2}{6}=\dfrac{1}{3}\)

1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6

=1/2-1/6

=3/6-1/6

=2/6=1/3

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}\)

\(=\dfrac{1}{2}-\dfrac{1}{6}\)

\(=\dfrac{1}{3}\)

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}=\dfrac{1}{2}-\dfrac{1}{6}=\dfrac{1}{3}\)

\(\frac{8}{14}+\frac{5}{12}+\frac{6}{14}+\frac{8}{12}-\frac{1}{12}\)

\(=\left(\frac{8}{14}+\frac{6}{14}\right)+\left(\frac{5}{12}+\frac{8}{12}-\frac{1}{12}\right)\)

\(=1+1=2\)

\(\frac{8}{14}+\frac{5}{12}+\frac{6}{14}+\frac{8}{12}-\frac{1}{12}\)

\(=\left(\frac{8}{14}+\frac{6}{14}\right)+\left(\frac{5}{12}+\frac{8}{12}-\frac{1}{12}\right)\)

\(=1+1=2\)

~ Hok tốt ~

\(\frac{8}{14}+\frac{5}{12}+\frac{6}{14}+\frac{8}{12}-\frac{1}{12}\)

\(=\left(\frac{8}{14}+\frac{6}{14}\right)+\left(\frac{5}{12}+\frac{8}{12}-\frac{1}{12}\right)\)

\(=1+1\)

\(=2\)

Hướng dẫn giải:

a. 88 + 75 + 12 = (88 + 12) + 75 = 100 + 75 = 175

b. 146 + 55 + 54 = (146 + 54) + 55 = 200 + 55 = 255.

 o0                                                   rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr                           ẻu

\(-\dfrac{5}{14}:\dfrac{7}{17}-\dfrac{5}{14}:\dfrac{7}{11}-\dfrac{6}{7}=\dfrac{5}{14}:\left(-\dfrac{7}{17}\right)-\dfrac{5}{14}:\dfrac{7}{11}-\dfrac{6}{7}\)

\(=\dfrac{5}{14}.\left(-\dfrac{17}{7}\right)-\dfrac{5}{14}.\dfrac{11}{7}-\dfrac{6}{7}=\dfrac{5}{14}.\left(-\dfrac{17}{7}-\dfrac{11}{7}\right)-\dfrac{6}{7}\)

\(=\dfrac{5}{14}.\left(-4\right)-\dfrac{6}{7}=-\dfrac{10}{7}-\dfrac{6}{7}=-\dfrac{16}{7}\)

\(-\dfrac{5}{14}\) hay \(\dfrac{5}{14}\) vậy