A: This extra-curricular book has 56 pages.

2. Formula: 6÷36=6∶36= 1∶6.

A: The ratio of the tonnage of old yellow sand to the total tonnage of yellow sand is 1: 6.

3. Formula:1-2/9 = 7/91÷ 7/9 = 9: 7.

A: The ratio of planned investment to actual savings is 9: 7.

4. Formula: 20× 3/4 = 15 (g)

A: There is a piece of 18K gold jewelry, which weighs 20g and contains gold 15g.

5, 162× 1/6 = 27 (person) 27÷3=9 (person)

A: On average, there are 9 people in each class who can swim.

6. Formula: 15/2×30× 15=3375 (ton) 3500-3375= 125 (ton)

A: 30 trucks 15 times can't transport 3,500 tons of relief materials.

Note: these questions can be thought out with more brains. I will help you this time, but don't be lazy next time! Mathematics depends on quick thinking and more brains!