35 Clever Math Brain Teasers for Kids - Free Printable

Let's break down the riddle:

> "Multiply this number with any other number and you will get the same answer every time. What is the number?"

We are looking for a number that, when multiplied by any other number, always gives the same result — no matter what number you multiply it with.

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Step-by-step reasoning:

Let’s suppose the number we're looking for is $ x $.
Then, for any number $ a $, multiplying $ x \times a $ should give the same result, say $ R $.

So:
$$
x \times a = R \quad \text{for all } a
$$

Now consider two different values of $ a $, say $ a = 1 $ and $ a = 2 $:

- $ x \times 1 = R $
- $ x \times 2 = R $

But if both equal $ R $, then:
$$
x = R \quad \text{and} \quad 2x = R
$$

Substitute $ R = x $ into the second equation:
$$
2x = x \Rightarrow 2x - x = 0 \Rightarrow x = 0
$$

So the only number that satisfies this condition is 0.

Let’s test it:
- $ 0 \times 5 = 0 $
- $ 0 \times 100 = 0 $
- $ 0 \times (-3) = 0 $
- $ 0 \times 0 = 0 $

✔ Always gives the same answer: 0

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✔ Final Answer: 0

Because multiplying zero by any number always results in zero — the same answer every time.