Question:
If 5A x A = 399, then the value of A is
(a) 3
(b) 6
(c) 7
(d) 9
Solution:
(c) We have, 5A x A = 399
Here, A x A= 9 i.e. A x A is the number 9 or a number whose unit’s digit is 9. Thus, the number whose product with itself produces a two-digit
number having its unit’s digit as 9 is 7.
i.e. A x A = 49 => A=7
Now, 5 x A + 4 = 39
=> 5 x 7+4 = 39
So, A satisfies the product.
Hence, the value of A is 7.