i read in class 4 but I don't explain the answer
To solve this we are going to use formula for the future value of an ordinary annuity:
![FV=P[ \frac{(1+ \frac{r}{n} )^{nt} -1}{ \frac{r}{n} } ]](https://tex.z-dn.net/?f=FV%3DP%5B%20%5Cfrac%7B%281%2B%20%5Cfrac%7Br%7D%7Bn%7D%20%29%5E%7Bnt%7D%20-1%7D%7B%20%5Cfrac%7Br%7D%7Bn%7D%20%7D%20%5D)
where

is the future value

is the periodic payment

is the interest rate in decimal form

is the number of times the interest is compounded per year

is the number of years
We know from our problem that the periodic payment is $50 and the number of years is 3, so

and

. To convert the interest rate to decimal form, we are going to divide the rate by 100%


Since the interest is compounded monthly, it is compounded 12 times per year; therefore,

.
Lets replace the values in our formula:
![FV=P[ \frac{(1+ \frac{r}{n} )^{nt} -1}{ \frac{r}{n} } ]](https://tex.z-dn.net/?f=FV%3DP%5B%20%5Cfrac%7B%281%2B%20%5Cfrac%7Br%7D%7Bn%7D%20%29%5E%7Bnt%7D%20-1%7D%7B%20%5Cfrac%7Br%7D%7Bn%7D%20%7D%20%5D)
![FV=50[ \frac{(1+ \frac{0.04}{12} )^{(12)(3)} -1}{ \frac{0.04}{12} } ]](https://tex.z-dn.net/?f=FV%3D50%5B%20%5Cfrac%7B%281%2B%20%5Cfrac%7B0.04%7D%7B12%7D%20%29%5E%7B%2812%29%283%29%7D%20-1%7D%7B%20%5Cfrac%7B0.04%7D%7B12%7D%20%7D%20%5D)

We can conclude that after 3 years you will have $1909.08 in your account.
To find probability, you'd have to find the total number of marbles (5+3+6+6=20), and since there are 3 blue marbles, the probability of picking one is 3 out of 20, or 3/20
If that blue marble isn't replaced, there will then be 19 marbles, and 2 blue ones. So the probability of him picking another blue marble is 2/19
I have done this question before but i can’t remember