Solution: it takes x hours to get back to the upstream. 15x=25×3
x=5
The bear built a house out of wood, and it took him 28 minutes to saw the wood into five sections. According to this calculation, how long will it take to saw this piece of wood into eight sections?
Solution: Suppose it takes x minutes.
x:(8- 1)=28:(5- 1)
x=49
It takes 96 bricks to pave the floor with a square brick with a side length of 3 meters. If you change it into a square brick with a side length of 4 mm, how many pieces do you need?
Solution: Suppose X blocks are needed.
4×4×x=3×3×96
x=54
4. The small animals in the forest gathered together to congratulate the little bear on building a new house. They lined up for group dancing. If each line has 20 stops, it is exactly 12 lines. If there are 24 stops on each line, how many lines can you stand?
Solution: Suppose we can stand in X rows.
24x=20× 12
x= 10
Extension and expansion
5. Teacher Zhang went to buy gifts for June 1st. The money he brought with him can buy 20 yo-yos at the original price. Now this kind of ball is sold at a 20% discount. How many yo-yos can Teacher Zhang buy now?
Solution: Let each yo-yo be 1 yuan.
20 divided by (1+20%)=25 (pieces) 25-20=5 (pieces)
6. No more questions
Method 1: 100 times 15 divided by 120 = 12.5 (hours).
Method 2: Solution: It takes X hours to set up the whole process.
100× 15= 120X
X= 12.5
A: Yes. . . . . . . .