Answers

2014-03-11T20:33:57+08:00
3 coins could land in any of these ways: 
HHH 
HHT 
HTH 
THH 
TTH 
THT 
HTT 
TTT 

Those that have at least 2 heads are shown below: 
HHH, HHT, HTH, THH <= that's 4 out of 8 for a 50% or 1/2 probability 
The probability of having at most 2 heads is 7/8, based on these choices: 
HHT, HTH, THH, TTH, THT, HTT, TTT <= That's 7 of 8 or 87.5% 
I hope that helps!! :-
0