A number between 10 and 100 is five times the sum of its digits. If 9 ...
Given information:
- A number between 10 and 100 is five times the sum of its digits.
- If 9 is added to it, the digits are reversed.
To find: The number
Solution:
Let the number be represented by 'xy', where x and y are the digits.
According to the first condition, we can write:
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xy = 5(x + y)
Simplifying the second equation, we get:
xy = 5x + 5y
xy - 5x - 5y = 0
x(y - 5) - 5y = 0
x(y - 5) = 5y
Since x and y are digits, y cannot be zero. Hence, we can divide both sides by y:
x(y - 5) / y = 5
Expanding the left side:
x - (5x / y) = 5
Since x and y are digits, 5x / y can only be 0, 5, 10, 15, or 20.
- If 5x / y = 0, then x = 5, which is not possible since x is a digit between 1 and 9.
- If 5x / y = 5, then x = y, which gives the number 11. However, this number does not satisfy the condition that it is between 10 and 100.
- If 5x / y = 10, then x = 2y, which gives the number 25. However, this number does not satisfy the condition that it is between 10 and 100.
- If 5x / y = 15, then x = 3y, which gives the number 35. However, this number does not satisfy the condition that it is between 10 and 100.
- If 5x / y = 20, then x = 4y, which gives the number 45. This number satisfies both conditions.
Now, we need to check if adding 9 to 45 gives us the reversed digits.
45 + 9 = 54
Therefore, the answer is option C, 45.
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