10-( 10× 10-87)÷( 10+3)
= 10- 13÷ 13
= 10- 1
=9 (question)
② Xiaohong got it right:
10-( 100-74)÷ 13
= 10-26÷ 13
= 10-2
=8 (question)
③ Xiaohua got it right:
10-( 100-9)÷ 13
= 10-9 1÷ 13
= 10-7
=3 (question)
④ Three people and one * * * Correct answer: 9+8+3=20 (question).
A: Three people answered 20 questions correctly.
So the answer is: 20.