Among the 12 solar collectors on display at trade show 9 are

Among the 12 solar collectors on display at trade show, 9 are flat-plate collectors and thd rest of concentrating collectors. In person visiting the show randomly selects 4 of solar collectors to impact, what is the probability that 3 of them will be flat-plate collectors?

Solution

There are 12C4 ways to select any four.

There are 9C4 ways to select only flat plate collectors.

Thus,

P(all flat plate) = 9C4 / 12C4 = 0.254545455 [answer]