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Shanghai mathematics textbooks are all practiced.
Ideas:

1, what is three times the circumference of a circular cowshed (around three times)? 2. The cowshed is closed, and the number of stakes at the separation point is equal to the number of divided sections. There are as many stakes as 2 meters in the circumference (single circle).

Solution:

C=2πr

2×3. 14× 15×3=282.6﹙m﹚

2× 3. 14× 15 ÷ 2 ≈ 47 ≈ radical.

Answer: The cowshed should be surrounded by 282.6-meter-thick iron wire for three times. If you install a stake every 2 meters, you need to install about 47 stakes.