Solution: Let Li Ming take X this time, so the average score of the last (x- 1) exam is 88.
Then (x- 1)*88+ 100=x*90.
88x-88+ 100=90X
Interchange of terms
2x= 12
The solution is x=6.
Through the substitution test, this exam is the sixth time, and I got 88 points in the first 6- 1=5 times, so the total score is 88*5=440.
The total score of the first six times is 88*5+ 100=540.
Average score =540/6=90
Meet the requirements of the topic and answer correctly.
A: This is the sixth exam.