Some circle problems! Write the formula! From 10 am to 2 pm, how many centimeters does the tip of the 1 cm minute hand on the watch turn? The circumference of the semicircle is 30.84 cm. What is its radius? How many centimeters of rope is required to tie two glass bottles with a bottom diameter of 5 cm together?

Some circle problems! Write the formula! From 10 am to 2 pm, how many centimeters does the tip of the 1 cm minute hand on the watch turn? The circumference of the semicircle is 30.84 cm. What is its radius? How many centimeters of rope is required to tie two glass bottles with a bottom diameter of 5 cm together?

(1) After four hours from 10:00 to 14:00, the minute hand turns four times
Four circle length = π (2R) × 4
=π×（2×1）×4
=8π
≈25.12（cm）
（2）30.84÷（2+π）
≈30.84÷5.14
=6（cm）
（3）5π+5×2
≈15.7+10
=25.7（cm）
Note: π is taken as 3.14

Primary school mathematics chicken and rabbit with cage deformation problem, formula method, seek detailed explanation
It is said that the "nine headed bird" has nine tails and one head, and the "nine tailed bird" has nine tails and one head. If there are 288 heads and 432 tails, how many are the "nine headed bird" and the "nine tailed bird"?
Note: to calculate the formula method,

One nine headed bird + one nine tailed bird = 10 heads and 10 tails. When the number of nine headed birds and nine tailed birds is equal, the head and tail are equal. For each additional nine tailed bird, the tail is 8 more than the head. Now the number of nine tailed birds is more than nine headed birds (432-288) / 8 = 18. Remove these 18 nine tailed birds, the number of the remaining nine headed birds is equal to nine tailed birds, and the number of the remaining heads is 288-18