A number has two digits. The digit at tens place is four times the digit at units place. If 54 is subtracted from the number, the digits are reversed. Find the original number.

"The digit at tens place is four times the digit at units place."

How many possible numbers are there?

1 in the units place: 41

2 in the units place: 82

If you try 3 in the units place, 4 * 3 = 12, you'd get 123, and now it's a three-digit number, so the only possibilities are 41 and 82.

41 or 82

If you subtract 54 from 41, you get a negative number, so 41 cannot be the number.

82 - 54 = 28, which has the digits of 82 in reverse order.

Answer: 82