Bonita said that the product of 56 × 123 is 73. how can you tell that her answer is wrong?

She may have used a wrong operation to get this answer. 73 is not the correct answer, and you can prove it using a calculator or longhand. The correct answer is 6888.

Without doing any math, you know her answer is wrong. 
1) Think of a smaller problem. 10 x 10 is 100, already bigger than what Bonita said. In her question, what was being multiplied together were both bigger than 10, so already we know Bonita's not right. 
2) Think through what she said. 56 123's is something less than one of the numbers. How does that work? It doesn't.
Hope this helps!