Question

I thought of a two-digit number. The unit digit of my number is a prime number, and the tens digit is four times as big as the unit digit. What is my number?
Please help! I'm very bad at these "what's my number" problems, so please respond ASAYC! (as soon as you can)

Answer 1

Answer:  82

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Explanation:

Let A be the tens digit and B be the units digit

We can write the number as AB. So if A = 9 and B = 2 for instance, then the number is AB = 92. Keep in mind I'm not multiplying A and B here.

"The unit digit is a prime" means B could be any of these values {2,3,5,7}. We only list the single digit primes. The value 1 is not prime.

Now multiply each of those items by 4

4*2 = 8

4*3 = 12

4*5 = 20

4*7 = 28

Of those results, only 4*2 = 8 leads to a single digit answer.

This must mean that A = 8 and B = 2

Therefore the number is AB = 82.