We must find UNIQUE combinations because choosing a,b,c,d... is the same as d,c,b,a...etc. For this type of problem you use the "n choose k" formula...
n!/(k!(n-k)!), n=total number of choices available, k=number of choices made..
In this case:
20!/(10!(20-10)!)
20!/(10!*10!)
184756
Answer:
(-2,1),(-1,2),(-3,5/3)
Step-by-step explanation:
Hello there! I can help you! The formula for compound interest is P(1 + r)^t, where P= principal (initial amount), r = interest rate (in decimal form), and t = time (in years). Let's do this step by step. First off, we add the rate into 1. 4% is the interest rate (0.04 in decimal form). 1 + 0.04 is 1.04. Now, what we will do is raise that number to the 2nd power, because the time that elapses is 2 years. 1.04² is 1.0816. That's that. Now, multiply 7,500 to find the total amount of money. 1.0816 * 7,500 is 8,112. There. Toby's savings account balance in 2 years is £8,112.
Note: To solve for compound interest questions like it, add 1 to the percentage rate in decimal form, raise that number to a power based on the number of years (for example, raise the number to the 7th power if we are looking for the balance after 7 years), and then multiply that number by the starting amount. After you raise the number by a power, there may be a lot of numbers behind it. Whatever you do, DO NOT delete the number. Keep it there and multiply it by the principal.
