"There are 15 questions on an exam. In how many ways can the exam be answered with exactly 8 answers correct?"

Mathematics

1 answer:

erastovalidia [21]3 years ago

5 0

Answer:

The exam can be answered with exactly 8 answers correct in 6435 ways.

Step-by-step explanation:

The order is not important.

For example, answering correctly the questions 1,2,3,4,5,6,7,8 is the same outcome as answering 2,1,3,4,5,6,7,8. So we use the combinations formula to solve this problem.

Combinations formula:

$C_{n,x}$ is the number of different combinations of x objects from a set of n elements, given by the following formula.

$C_{n,x} = \frac{n!}{x!(n-x)!}$

"There are 15 questions on an exam. In how many ways can the exam be answered with exactly 8 answers correct?"

Combinations of 8 questions from a set of 15. So

$C_{15,8} = \frac{15!}{8!(15-8)!} = 6435$

The exam can be answered with exactly 8 answers correct in 6435 ways.

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$650 is invested in an account earning 8.6% interest (APR), compounded monthly. Write a function showing the value of the accoun

IRISSAK [1]

Answer:

The value of the acount after t years is of $A(t) = 650(1.0072)^{12t}$

The annual growth rate is of 0.72%.

Step-by-step explanation:

Compound interest:

The compound interest formula is given by:

$A(t) = P(1 + \frac{r}{n})^{nt}$

Where A(t) is the amount of money after t years, P is the principal(the initial sum of money), r is the interest rate(as a decimal value), n is the number of times that interest is compounded per year and t is the time in years for which the money is invested or borrowed.

$650 is invested in an account earning 8.6% interest (APR), compounded monthly.

This means that $P = 650, r = 0.086, n = 12$ . So