Discussion

What is the unit digit of \(137^{13} \times 13!\) ?

Answer: A

We look at the unit digit of each part of the product. The unit digit of 13! is 0, because 13 is greater than 5, so 13! contains factors of 2 and 5. Any number multiplied by a number ending in 0 will also end in 0. Therefore, the unit digit of the entire expression is 0, regardless of the unit digit of \(137^{13}\).