God, you still ask this question in three parts, or you won't ask a page for nothing.

Stop talking nonsense:

Assuming that the monitor is wrong, the probability that Xiao Ming gets the correct answer is: 90%×90%=8 1%.

Assuming that the monitor heard wrong, the probability of Xiao Ming getting the correct answer is:10% ×10% =1%.

So the probability of Xiao Ming getting the correct answer is: 8 1%+ 1%=82%.