Bella keeps a supply of red, blue, and black pens in a drawer. The drawer has 17 red pens, 18 blue pens, and 11 black pens. If Bella wants a red pen, what is the minimum number of pens she has to pull out from the drawer to make sure she gets a red pen?

Think. If all the black and blue pens are drawn first, how many is that? The next pen MUST be a red one.

To determine the minimum number of pens Bella has to pull out from the drawer to ensure she gets a red pen, we need to consider the worst-case scenario. This means assuming that Bella draws all the non-red pens before finally getting a red one.

Given Bella's initial supply of pens in the drawer:
- There are 17 red pens, which means there are 17 chances of drawing a red pen.
- There are a total of 17 + 18 + 11 = 46 pens in the drawer.

In the worst-case scenario, Bella would draw all 46 pens without getting a red pen. Therefore, she would need to pull out at least 47 pens from the drawer to guarantee that she gets a red pen.

Hence, the minimum number of pens Bella has to pull out from the drawer to ensure she gets a red pen is 47.