What is the **unit digit** of the sum of the first 150 whole numbers?

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**Solution:**

1. The first 150 whole numbers are from 0 to 149.

2. The sum of first *n* whole numbers is given by the formula:
   $$	ext{Sum} = \frac{n(n-1)}{2}$$
   However, since whole numbers start from 0, the sum of first 150 whole numbers (0 to 149) is:
   $$	ext{Sum} = \frac{149 	imes 150}{2}$$

3. Calculate the sum:
   $$\frac{149 	imes 150}{2} = 149 	imes 75 = 11175$$

4. The unit digit of 11175 is **5**.

**Answer:** 5

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