5A × A = 399 then the value of A = ……………… A) 3 B) 7 C)

1.	5A × A = 399 then the value of A = ……………… A) 3 B) 7 C) 4 D) 6
Answer» Correct option is (B) 7 5A \(\times\) A = (50+A) A = \(A^2+50A\) \(\therefore\) 5A \(\times\) A = 399 \(\Rightarrow\) \(A^2+50A\) = 399 \(\Rightarrow\) \(A^2+50A-399=0\) \(\Rightarrow\) \(A^2+57A-7A-399=0\) \(\Rightarrow\) A(A+57) - 7(A+57) = 0 \(\Rightarrow\) (A-7) (A+57) = 0 \(\Rightarrow\) A - 7 = 0 or A+57 = 0 \(\Rightarrow\) A = 7 or A = -57 \(\Rightarrow\) A = 7 \((\because\) Middle digit in a number never be negative) Correct option is B) 7

5A × A = 399 then the value of A = ……………… A) 3 B) 7 C) 4 D) 6

Answer»

Correct option is (B) 7

5A \(\times\) A = (50+A) A

= \(A^2+50A\)

\(\therefore\) 5A \(\times\) A = 399

\(\Rightarrow\) \(A^2+50A\) = 399

\(\Rightarrow\) \(A^2+50A-399=0\)

\(\Rightarrow\) \(A^2+57A-7A-399=0\)

\(\Rightarrow\) A(A+57) - 7(A+57) = 0

\(\Rightarrow\) (A-7) (A+57) = 0

\(\Rightarrow\) A - 7 = 0 or A+57 = 0

\(\Rightarrow\) A = 7 or A = -57

\(\Rightarrow\) A = 7 \((\because\) Middle digit in a number never be negative)

Correct option is B) 7