Answer:
36
Step-by-step explanation:
I would label the 8 different cellphones: A, B, C, D, E, F, G, H.
Here is a list of all the possible ways to group these letters together, starting with A then B, and so on:
ab bc cd de ef fg gh
ac bd ce df eg fh
ad be cf dg eh
ae bf cg dh
a f bg ch
ag bh
ah
As you can see, the number of pairs going from left to right decreases by one every column all the way until 1. Note that any two letters that are reversed does not make it a new combination.
Total number of ways a group of two cell phones can be selected =
8+7+6+5+4+3+2+1 = 36!
