Mario has received 16 unlabeled thumb-drives with ads on them. he has 8 gray drives which have the print ad, 4 pink drives which have the digital display ad, and 4 blue drives with the video ad. what is the minimum number of thumb-drives he must open to ensure that he has one of each color with each ad? *

Mario has 8 gray drives which have the print ad, 4 pink drives which have the digital display ad, and 4 blue drives with the video ad.

The most unsuccessfull way of opening drives is: 1st - grey, 2nd - grey, 3 - rd grey and so on untill all 8 gray drives are opened, then 9th - pink, 10th - pink, 11th - pink, 12th - pink  (or 4 blue) and then blue one (or pink one) drive.

He must open 13 drives to ensure that he has one of each color with each ad.

When i did the math i got 11 cm