There are 3 blue pens, 4 red pens and 5 yellow pens in a box. Without looking, I take pens from the box one by one. How many pens do I need to take from the box to be certain that I have at least one pen of each colour?
A 8
B 9
C 10
D 11
E 12
12
To determine the minimum number of pens you need to take from the box to be certain that you have at least one pen of each color, we can analyze the worst-case scenario.
Let's assume the worst-case scenario is that you first pick all the blue pens, then all the red pens, and finally all the yellow pens.
In this scenario, you would need to take all the 3 blue pens, followed by the 4 red pens, and finally the 5 yellow pens.
So the minimum number of pens you would need to take from the box to be certain that you have at least one pen of each color is:
3 (blue pens) + 4 (red pens) + 5 (yellow pens) = 12 pens
Therefore, the correct answer is E) 12.