If 5A x A = 399,

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.

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