On a ten question true-false quiz what is the probability of getting 70 percent or more correct by just guessing each answer?

Probability, P, of 70% or more correct (7 or more correct) is: P(7) + P(8) + P(9) + P(10). See the related link; N=10, P = 0.5, and K = 7, 8, 9, & 10. Therefore the probability is: .11719 + .04395 + .00977 + .00098 = .17189 or approximately 17.2% probability 7 or more correct.