:V....

A

18 số:

12 số\(\left\{{}\begin{matrix}123;125;143;145\\321;325;341;345\\521;523;541;543\end{matrix}\right.\)

6 số \(\left\{{}\begin{matrix}214;234;254\\412;432;452\end{matrix}\right.\)

\(\Rightarrow\) Có: 12 + 6 = 18 (số)

a)      2x = 102

         x = 102 : 2

         x = 51

b)     x + 19 = 301

        x = 301 - 19

        x = 282

c) 93 – x = 27

     x = 93 - 27

     x = 66

(x+1) + (x+2) + (x+3) +....+ (x+100) = 5750

x + 1 + x + 2 + x + 3 +...+ x + 100 = 5750

(x + x + x +...+ x) + (1 + 2 + 3 +...+ 100) = 5750

100x + 5050 = 5750

100x = 5750 - 5050

100x = 700

x = 700 : 100

x = 7

Thử liệt kê 12 số đấy ra xem

18 mà :V

18

D

20 - 2 (x + 4) = 4

2 (x + 4) = 20 - 4

2 (x + 4) = 16

x + 4 = 16 : 2

x + 4 = 8

x = 8 - 4

x = 4