( X x 81 + 2 x 81 - 3530 ) x 21 = 714

      X x 81 + 2 x 81 - 3530        = 714 : 21

      X x  81 + 2 x 81 - 3530       = 34

      X x 81 + 2 x 81                    = 34 +3530

      X x 81 + 2 x 81                    = 3564

      ( X + 2 ) x 81                        = 3564

         X + 2                                  = 3564 : 81

         X + 2                                  = 44

         X                                        = 44 - 2

         X                                         = 42

h nha Lucy heartfilia

Ta có: 320 x 25 + 125 x 56 

      =  320 x 25 + 25 x (5 x 56)

      = 320 x 25 + 25 x 280

     = 25 x (320 + 280) 

      = 25 x 600

      = 15 000

Từ 1-> 2014 có:2014-1+1=2014(số)

=>1+2+3+4+....+2014=(2014+1)x2014:2=2029105

Vậy...........

I don now!

45% của 100 là :

45% x 100 = 45

Đáp số : 45

\(\frac{1}{5.8}+\frac{1}{8.11}+\frac{1}{11.14}+...+\frac{1}{x\left(x+3\right)}=\frac{1}{18}\)

\(\Leftrightarrow\frac{1}{3}.\left(\frac{3}{5.8}+\frac{3}{8.11}+\frac{3}{11.14}+.....+\frac{3}{x\left(x+3\right)}\right)=\frac{1}{18}\)

\(\Leftrightarrow\frac{1}{3}.\left(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+....+\frac{1}{x}-\frac{1}{x+3}\right)=\frac{1}{18}\)

\(\Leftrightarrow\frac{1}{3}.\left(\frac{1}{5}-\frac{1}{x+3}\right)=\frac{1}{18}\Leftrightarrow\frac{1}{5}-\frac{1}{x+3}=\frac{1}{18}:\frac{1}{3}=\frac{1}{6}\)

\(\Leftrightarrow\frac{1}{x+3}=\frac{1}{5}-\frac{1}{6}=\frac{1}{30}\)

<=>x+3=30

<=>x=27

Vậy x=27

11+22+33+44+55+66+77+88+99+111

= [11+99]+[22+88]+[33+77]+[44+66]+[55+111]

= 110+110+110+110+166

=440+166

=606

    3 x - x = 12

=> x * ( 3 - 1 ) =12 

=> x * 2 =12

=> x = 12 : 2

=> x = 6

Vậy x = 6

13 nữ ra về thì nam hơn 48

số nam là :

48 : (2-1) x 2 = 96 (bạn)

số nữ là:

48 : (2-1) x 1 + 12 = 61 (bạn)