[Math] In how many different ways can you invest 20,000 onto five funds in increments of 1,000

combinatorics

In how many different ways can you invest 20,000 onto five funds in increments of 1,000?

(Question 4.24 from Timothy Falcon Crack)

The answer says it is $5^{20}$, but I thought of this as a "stars and bars" type of problem and said it was $\binom{24}{4}$.

Where am I going wrong?

Best Answer

You are thinking that each $1000$ is identical, so all that matters is how much money you put into each fund. If they are, your answer is correct. $5^{20}$ would be correct if the $1000$s were distinct. If you invested $1000$ per month for $20$ months it matters which $1000$ goes into which fund. They are different problems with different answers. Check the wording of the problem for whether the $1000$s are identical or distinct.