Question

3x2=7 5x4=23 7x6=47 9x8=79 10x9=?

Answer 1

$(a\times b) = (a\times b) +(b -1) = c \\ \\ 3 \times 2 = (3\times 2) +(2-1) = 6 +1=7 \\ \\ 5 \times 4 = (5\times 4) +(4-1) = 20 +3=23 \\ \\ 7 \times 6 = (7\times 6) +(6-1) = 42 +5=47 \\ \\ 9 \times 8= (9\times 8) +(8-1) = 72 +7=79 \\ \\ \\ \\ 10 \times 9 = (10\times 9) +(9-1) = 90 +8=\boxed {\bf{98}}\\\sf {10\times 9 = \boxed{\bf {98}}}$