Assuming all the questions are done correctly, * * * should get 200 points. If making a mistake will reduce 13 points, then * * making a mistake (200- 109)/ 13=7.

Because Xiaoding scored 13 points more than Xiaoming, Xiaoding made one less mistake than Xiaoming.

So Xiaoding made three mistakes and Xiaoming made four.

So Xiaoding did the right thing for 7 and Xiaoming did the right thing for 6.

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