A) 5
B) 7
C) 6
D) 8
Correct Answer: D
Solution :
(d) Multiply as: \[(10A+2)\times (70+A)=6396\] \[\Rightarrow 700A+140+10{{A}^{2}}+2A=6396\] \[\Rightarrow 10{{A}^{2}}+702A+140=6396\] \[\Rightarrow 10{{A}^{2}}+702A-6256=0\] \[A=\frac{-702\,\underline{+\sqrt{{{\left( 702 \right)}^{2}}+40\times 256}}}{20}\] \[=-\frac{702+862}{20}=\frac{160}{20},\frac{-1564}{20}=8\] \[\therefore \,\,A=8\]
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