\(13,8:0,5+13,8:0,25+13,8:0,125\)
\(=13,8\times2+13,8\times4+13,8\times8\)
\(=13,8\times\left(2+4+8\right)\)
\(=13,8\times14\)
\(=193,2\)

Cần gấp

\(\dfrac{21}{17}\times\dfrac{13}{14}\times56\times\dfrac{3}{42}\)
\(=\dfrac{21}{17}\times\dfrac{13}{14}\times56\times\dfrac{1}{14}\)
\(=\dfrac{21\times13\times56}{17\times14\times14}\)
\(=\dfrac{3\times7\times13\times14\times2\times2}{17\times2\times7\times14}\)
\(=\dfrac{3\times13\times2}{17}\)
\(=\dfrac{78}{17}\)

Số học sinh đạt điểm 9,10 của lớp học:
\(40\times35:100=14\)(học sinh)
Số học sinh đạt điểm khá:
\(40\times45:100=18\)(học sinh)
Số học sinh đạt điểm trung bình:
\(40-14-18=8\)(học sinh)

Có ai trả lời cho mik ko ạ

A = 1/1 - 1/2 + 1/3 - 1/3 + 1/4

A = 1/1 - 1/4

A = 3/4

vậy A = 3/4

\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}\)

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

\(=1-\dfrac{1}{4}=\dfrac{4-1}{4}=\dfrac{3}{4}\)

\(101\times1,996-1,996\)
\(=\left(101-1\right)\times1,996\)
\(=100\times1,996\)
\(=199,6\)

101 x 1996 - 1996

= 101 x 1996 - 1996 x 1

= 1996 x (101 - 1) 

= 1996 x 100

= 199600

\(\dfrac{1}{42}+\dfrac{1}{30}+\dfrac{1}{12}+\dfrac{1}{6}+\dfrac{1}{2}\)
\(=\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{30}+\dfrac{1}{42}\)
\(=\dfrac{1}{1\times2}+\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{5\times6}+\dfrac{1}{6\times7}\)
\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}\)
\(=1-\dfrac{1}{4}+\dfrac{1}{5}-\dfrac{1}{7}\)
\(=\dfrac{140}{140}-\dfrac{35}{140}+\dfrac{28}{140}-\dfrac{20}{140}\)
\(=\dfrac{113}{140}\)

\(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{30}+\dfrac{1}{42}\)

\(=\dfrac{1}{2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{5.6}+\dfrac{1}{6.7}\)

\(=\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}\)

\(=1-\dfrac{1}{4}+\dfrac{1}{5}-\dfrac{1}{7}=\dfrac{140-35+28-20}{140}=\dfrac{113}{140}\)

Mình nghĩ đề bài cần thêm 1/20 mới tính nhanh được

\(\dfrac{5}{3}< x< \dfrac{7}{3}\)
\(\dfrac{5}{3}< \dfrac{x}{3}< \dfrac{7}{3}\)
\(x=\dfrac{6}{3}\)
\(x=2\)

vì 5/3 < x > 7/3 

=> x = 6/3 * hoặc x = 2 *