1, Teacher Wang presented awards to students with excellent academic performance. If everyone sends 2 diaries, there will be 13 more diaries; If you send three diaries to everyone, you will lose five. How many students have won prizes?

Number of people =( 13+5)÷(3-2)= 18 (people)

It costs 55.8 yuan to buy 6 pens and 8 pencils, and 30.3 yuan to buy 3 pens and 8 pencils. What is the unit price of pens and pencils?

Pen unit price =(55.8-30.3)÷(6-3)=25.5÷3=8.5 (Yuan)

Unit price of pencil =(55.8-6×8.5)÷8=4.8÷8=0.6 (Yuan)

3, a number, if its decimal part is expanded by 3 times, this number is 3.1; If the decimal part of it is expanded five times, the number is 4.5. What was the original number?

Fractional part =(4.5-3. 1)÷(5-3)=0.7.

Integer part =3. 1-0.7×3= 1

This number =0.7+ 1= 1.7.