Question

If 5A × A = 399, then the value of A is ______.

Options

• 3

• 6

• 7

• 9

Answer 1

If 5A × A = 399, then the value of A is 7.

Explanation:

We have, 5A × A = 399

Here, A × A = 9 i.e. A × 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 × A = 49 ⇒ A = 7

Now, 5 × A + 4 = 39

⇒ 5 × 7 + 4 = 39

So, A satisfies the product.

Hence, the value of A is 7.