4) *5* mà ⋮ (2 ; 3 và 5 ) là 150; 450;750

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Số 9995

a/

\(2A=8+2^3+...+2^{21}\)

\(2A-A=A=2^{21}+8-4-2^2=2^{21}\)

b/

\(3B=3^2+3^3+...+3^{101}\)

\(\Rightarrow3B-B=2B=3^{101}-3\)

\(\Rightarrow2B+3=3^{101}\)

200-18:(372:3.X-1)-28=166

200-18:(372:3.X-1)    =166+28

200-18:(372:3.X-1)    =194

200-18:(124.X-1)       =194

      18:(124.X-1)       =200-194

      18:(124.X-1)       =6

           124.X-1        =18:6

           124.X-1        =3

           124.X           =3+1

           124.X           =4

                 X           =4:124

                 X           =\(\frac{1}{31}\).