In this classic brain teaser, how many times can you subtract 10 from 100 before the operation no longer matches the original statement?

Introduction / Context:
This puzzle looks like a simple arithmetic question, but it is actually a trick riddle that tests your careful reading and logical reasoning. At first glance, many people try to compute how many times 10 can be taken away from 100, treating it as a division problem. However, the wording is specific: it asks how many times you can subtract 10 from 100, not from the changing result. Understanding this difference between the first subtraction from 100 and later subtractions from smaller numbers is the key to solving the riddle correctly.

Given Data / Assumptions:

• You start with the number 100.
• You repeatedly subtract 10 from the current value.
• The exact wording is "subtract 10 from 100", not "subtract 10 repeatedly until you reach zero".
• Basic arithmetic rules for subtraction are assumed to be known.

Concept / Approach:
The phrase "subtract 10 from 100" describes a very specific operation: 100 - 10. You can perform that exact operation only once, because after the first subtraction the number is no longer 100. Later subtractions are taken from 90, 80, 70 and so on, which means you are no longer subtracting 10 from 100 but from other values. The riddle plays on the difference between a strict reading of the expression and the intuitive idea of repeated subtraction or division by 10.

Step-by-Step Solution:
Step 1: Start with the initial number: 100. Step 2: Perform the first subtraction exactly as stated in the riddle: 100 - 10 = 90. Step 3: Observe that after this step, the current number is 90, not 100. Step 4: If you subtract 10 again, you now calculate 90 - 10, which is 80, so you are subtracting 10 from 90, not from 100. Step 5: Conclude that the operation "subtract 10 from 100" can only be done once, because after that the starting number is no longer 100.

Verification / Alternative check:
Another way to verify the answer is to compare two interpretations. If the question were purely about how many equal steps of 10 are needed to reduce 100 to 0, you would solve 100 / 10 = 10 and say ten times. But the riddle does not ask "How many times can you subtract 10 in total?" Instead, it literally asks how many times you can subtract 10 from 100. After the first subtraction, the phrase is no longer accurate because the number has changed. This confirms that the logically correct answer is "1 time".

Why Other Options Are Wrong:
9 times: This often comes from thinking about how many times you can move from 100 down to 10, but it still ignores the exact wording about starting from 100 each time.
10 times: This is the result of treating the problem like 100 / 10, but later subtractions are from 90, 80, 70, etc., not from 100.
0 times: You definitely can subtract 10 from 100 once, so 0 is incorrect.
As many times as you like: While you can keep subtracting 10 from the changing result, you cannot keep subtracting 10 from 100 specifically. The riddle is not about infinite repetition.

Common Pitfalls:
The most common mistake is to switch unconsciously from a precise language interpretation to a pure arithmetic sequence. Many test takers immediately think "100 divided by 10 equals 10" and choose 10 times without considering that only the first subtraction is truly "from 100". Others may rush and simply guess between 9 and 10 without rereading the puzzle. To avoid this, always pay close attention to wording in verbal reasoning questions and check whether the phrase must remain literally true after each step. Once you get used to this style of riddle, you will spot the trick quickly.

Final Answer:
You can subtract 10 from 100 only 1 time, because after that, the number is no longer 100.