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Question
If 5A × A = 399, then the value of A is ______.
Options
3
6
7
9
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Solution
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.
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