Đáp án đúng: B
Giải chi tiết:+ Tính A:
\(\begin{array}{l}A:6 + 23 = 30\\A:6\,\,\,\,\,\,\,\,\,\,\, = 30 - 23\\A:6\,\,\,\,\,\,\,\,\,\,\, = \,\,7\\A\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 7 \times 6\\A\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \,42\end{array}\)
+ Tính B:
\(\begin{array}{l}B:7 = 35:7 + 3\\B:7 = 5 + 3\\B:7 = 8\\B\,\,\,\,\,\,\, = 8 \times 7\\B\,\,\,\,\,\,\, = 56\end{array}\)
+ Tính C:
\(\begin{array}{l}C:5 = 14\\C\,\,\,\,\,\,\, = 14 \times 5\\C\,\,\,\,\,\,\, = 70\end{array}\)
+ Tính D:
\(\begin{array}{l}D:2 + 30 = 50\\D:2\,\,\,\,\,\,\,\,\,\,\, = 50 - 30\\D:2\,\,\,\,\,\,\,\,\,\,\, = 20\\D\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 20 \times 2\\D\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 40\end{array}\)
Vậy \(A = 42;\,B = 56;\,C = 70;\,D = 40\)
Chọn B