Xiaohua took part in the city math competition, with 12 questions. He got a score of 10 if he did a correct question, and a score of 4 if he did a wrong question. Xiaohua got 78 points in the exam. How many questions did Xiaohua do right? Xiaohua took part in the city math competition, with 12 questions. He got a score of 10 if he did a correct question, and a score of 4 if he did a wrong question. Xiaohua got 78 points in the exam. How many questions did Xiaohua do right?

Solution:

Score of all answers: 12× 10= 120.

Actual score: 78 points

Score difference: 120-78=42 points.

Change a correct question into a wrong question, and the score difference is: 10+4= 14.

Number of wrong questions: 42÷ 14=3

Number of correct questions: 12-3=9.

Xiaohua answered nine questions correctly.