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.