982 671 904 - 1000 = 982 670 904

C

cháu quen dùng rồi (ntd đây nè )

Gọi số cần tìm là A

\(\text{Ax}5+10-12=48\\ \text{Ax}5+10=12+48\\ \text{Ax}5+10=60\\ \text{Ax}5=60-10\\ \text{Ax}5=50\\ =>A=10\)

Vậy số cần tìm là 10

\(172x81+828x81\\ =81\left(172+828\right)\\ 81x1000=81000\)

\(X\text{∈}B\left(11\right)=\left\{11;22;33\right\}\)

\(A=2^1+2^2+2^3+...+2^{39}+2^{40}\\ 2^1A=2^2+2^3+2^4+...+2^{40}+2^{41}\\ \)

\(2^1A-A=A=\left(2^2+2^3+2^4+...+2^{40}+2^{41}\right)-\left(2^1+2^2+2^3+...+2^{40}+2^{41}\right)\\ A=2^{41}-2^1\)