The three coins could land any these 8 ways:
HHH, HHT, HTH, HTT, THH, THT, TTH, TTT
P(3 heads) = 1 way out of 8  or 1/8
P(2 heads) = 3 ways out of 8 or 3/8
P(1 head) = 3 ways out of 8 or 3/8
P(0 heads) = 1 way out of 8 or 1/8
 x=Winnings  P(x)  E(x)=x�P(x)
     $3      1/8      $.375
     $2      3/8      $.75
     $1      3/8      $.375
   -$10      1/8     -$1.25
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Total expectation =   $ .25