Can be 64321 --> 1 way
How can we 3C2 yet it is an arrangement.
I only find 76432, 76421 as the only viable options. I do not know about 764231 Please explain why we have this
Can be 764XX --> 3C2 ways = 3!/2!1! = 3 ways
Because the last two places can be taken by any of the 3 remaining models who are shorter than 4. We cannot take 5 as that would mean model 6 and model 4 would not be standing side by side.
Since we have 3 models and only 2 places, the number of ways to pick a pair of 2 models from a pool of 3, is 3C2.
In case you were interested, the 3 ways to do it: