Answer:
![\boxed{4 \sqrt[8]{ {d}^{3} } }](https://tex.z-dn.net/?f=%20%5Cboxed%7B4%20%5Csqrt%5B8%5D%7B%20%7Bd%7D%5E%7B3%7D%20%7D%20%7D%20)
Step-by-step explanation:
![= > 4 {d}^{ \frac{3}{8} } \\ \\ = > 4({d}^{3 \times \frac{1}{8} }) \\ \\ = > 4( {d}^{3} \times {d}^{ \frac{1}{8} } ) \\ \\ = > 4( {d}^{3} \times \sqrt[8]{d} ) \\ \\ = > 4 \sqrt[8]{ {d}^{3} }](https://tex.z-dn.net/?f=%20%3D%20%20%3E%204%20%7Bd%7D%5E%7B%20%5Cfrac%7B3%7D%7B8%7D%20%7D%20%20%20%5C%5C%20%20%5C%5C%20%3D%20%20%20%3E%204%28%7Bd%7D%5E%7B3%20%5Ctimes%20%20%5Cfrac%7B1%7D%7B8%7D%20%7D%29%20%5C%5C%20%20%5C%5C%20%20%3D%20%20%3E%204%28%20%7Bd%7D%5E%7B3%7D%20%20%5Ctimes%20%20%20%7Bd%7D%5E%7B%20%5Cfrac%7B1%7D%7B8%7D%20%7D%20%29%20%5C%5C%20%20%5C%5C%20%20%3D%20%20%3E%204%28%20%7Bd%7D%5E%7B3%7D%20%20%5Ctimes%20%20%5Csqrt%5B8%5D%7Bd%7D%20%29%20%5C%5C%20%20%5C%5C%20%20%3D%20%20%3E%204%20%20%5Csqrt%5B8%5D%7B%20%7Bd%7D%5E%7B3%7D%20%7D%20)
The string would have to be 4 feet long to have a frequency of 400cps because each foot=100cps
We are choosing 2
2
r
shoes. How many ways are there to avoid a pair? The pairs represented in our sample can be chosen in (2)
(
n
2
r
)
ways. From each chosen pair, we can choose the left shoe or the right shoe. There are 22
2
2
r
ways to do this. So of the (22)
(
2
n
2
r
)
equally likely ways to choose 2
2
r
shoes, (2)22
(
n
2
r
)
2
2
r
are "favourable."
Another way: A perhaps more natural way to attack the problem is to imagine choosing the shoes one at a time. The probability that the second shoe chosen does not match the first is 2−22−1
2
n
−
2
2
n
−
1
. Given that this has happened, the probability the next shoe does not match either of the first two is 2−42−2
2
n
−
4
2
n
−
2
. Given that there is no match so far, the probability the next shoe does not match any of the first three is 2−62−3
2
n
−
6
2
n
−
3
. Continue. We get a product, which looks a little nicer if we start it with the term 22
2
n
2
n
. So an answer is
22⋅2−22−1⋅2−42−2⋅2−62−3⋯2−4+22−2+1.
2
n
2
n
⋅
2
n
−
2
2
n
−
1
⋅
2
n
−
4
2
n
−
2
⋅
2
n
−
6
2
n
−
3
⋯
2
n
−
4
r
+
2
2
n
−
2
r
+
1
.
This can be expressed more compactly in various ways.
calculatorsoup is a website that answers math problems it may be able to answer this one
