There are 15 + 7 + 9 + 6 = 37 total stickers. Of those, 15 + 9 = 24 are small and 15 + 7 = 22 are stars. However, there are 15 small stars so 24 - 15 = 9 of them are only small and 22 - 15 = 7 are only stars. This means that there are 15 + 9 + 7 = 31 stickers that are small or stars, therefore the probability is 31/37.
For the most part, the cross-section formed is a <em>trapezoid</em>, but if the slice passes through the apex of the pyramid, that shape is a <em>triangle</em>.
