Đáp án đúng: A
Phương pháp giải:
Áp dụng quy tắc tìm số bị trừ, thừa số chưa biết, số bị chia,…
Sử dụng quy tắc: Chuyển vế - Đổi dấu.Giải chi tiết:a) \(x - 25 = 65\)
\(\begin{array}{l}x - 25 = 65\\x\,\,\,\,\,\,\,\,\,\,\,\,\, = 65 + 25\\x\,\,\,\,\,\,\,\,\,\,\,\,\, = 90\end{array}\)
Vậy \(x = 90\).
b) \(35.\left( {27 - x} \right) = 70\)
\(\begin{array}{l}35.\left( {27 - x} \right) = 70\\\,\,\,\,\,\,\,\,\,\,\,27 - x\,\,\, = 70:35\\\,\,\,\,\,\,\,\,\,\,\,27 - x\,\,\, = 2\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = 27 - 2\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = 25\end{array}\)
Vậy \(x = 25\).
c) \(\left( {x - 140} \right):7 = {3^3} - {2^3}.3\)
\(\begin{array}{l}\left( {x - 140} \right):7 = {3^3} - {2^3}.3\\\left( {x - 140} \right):7 = 27 - 8.3\\\left( {x - 140} \right):7 = 27 - 24\\\left( {x - 140} \right):7 = 3\\\,x - 140\,\,\,\,\,\,\,\,\,\,\, = 3.7\\\,x - 140\,\,\,\,\,\,\,\,\,\,\, = 21\\\,x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 21 + 140\\\,x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 161\end{array}\)
Vậy \(x = 161\).
d) \({2^x}:{2^5} = 4\)
\(\begin{array}{l}{2^x}:{2^5} = 4\\{2^x}:{2^5} = {2^2}\\{2^x}\,\,\,\,\,\,\,\,\,\, = {2^2}{.2^5}\\\,{2^x}\,\,\,\,\,\,\,\,\, = {2^7}\\ \Rightarrow x = 7\end{array}\)
Vậy \(x = 7\).