56-4x7= 56-28                      50:5+25=10+25           27:3+16=9+16              27+25x5=27+125         4x7-16=28-16       42-6x4=42-24

            = 28                                         =35                              =25                                =152                          =12                       = 18

\(\left(4+5+1\right)\times\dfrac{7}{10}=10\times\dfrac{7}{10}=\dfrac{70}{10}=7\)

(4+5+1).7/10

=10.7/10

=7

7

`2/[1xx4]+2/[4xx7]+...+2/[97xx100]`

`=2/3xx(3/[1xx4]+3/[4xx7]+...+3/[97xx100])`

`=2/3xx(1-1/4+1/4-1/7+...+1/97-1/100)`

`=2/3xx(1-1/100)=2/3xx99/100=33/50`

\(\dfrac{2}{1.4}+\dfrac{2}{4.7}+...+\dfrac{2}{97.100}\)

\(=\dfrac{2}{3}.\left(\dfrac{3}{1.4}+\dfrac{3}{4.7}+...+\dfrac{3}{97.100}\right)\)

\(=\dfrac{2}{3}.\dfrac{99}{100}\)

\(=\dfrac{33}{50}\)

\(\dfrac{2}{1.4}+\dfrac{2}{4.7}+...+\dfrac{2}{97.100}\)

\(=\dfrac{2}{3}.\left(\dfrac{3}{1.4}+\dfrac{3}{4.7}+...+\dfrac{3}{97.100}\right)\)

\(=\dfrac{2}{3}.\left(\dfrac{1}{1}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\)

\(=\dfrac{2}{3}.\left(\dfrac{1}{1}-\dfrac{1}{100}\right)\)

\(=\dfrac{2}{3}.\left(\dfrac{100-1}{100}\right)\)

\(=\dfrac{2}{3}.\dfrac{99}{100}\)

\(=\dfrac{1}{1}.\dfrac{33}{50}\)

\(=\dfrac{33}{50}\)

ai yêu tui kb nha

4A=1.2.3.4+2.3.4(5-1)+3.4.5(6-2)+.....+98.99.100(101-97)

4A=1.2.3.4+2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+....+98.99.100.101-97.98.99.100

4A=98.99.100.101

A=(98.99.100.101):4=24497550

4×7-4×2=4×(7-2)

               =4×5=20

Đáp án là 20 nhé