Question

Brian claims that his dog can do single-digit multiplication. He shows the dog 10 cards with simple multiplication problems that are either correct or incorrect. The dog correctly identifies the correctness of the card 7 times out of 10. If the dog were simply guessing, how many would the dog be expected to get correct?

Answer 1

x^2-2x=-1, 3x-x-x+a-a=5, (x^2-1)/(x+1), 2x-(x+x)

Answer 2

for each trial :
P(Success) = 1/2
P(Fail) = 1/2

Answer 3

expected value = n*p = 10*1/2 = 5

Answer 4

oh okay thank you !