Sam invests a sum of money in a retirement account with a fixed annual interest rate of 7% compounded quarterly. After 13 years, the balance reaches $19,280.02. What was the amount of
the initial investment? ROUND YOUR ANSWER TO THE NEAREST DOLLAR (do NOT put a dollar
sign $ in your answer)

The initial amount of investment was $7,822

Step-by-step explanation:

The formula for compound interest, including principal sum is:

, where

Let us use this rule to solve the question

∵ Sam invests a sum of money in a retirement account with a fixed

   annual interest rate of 7% compounded quarterly

∴ r = 7% = = 0.07

∴ n = 4 ⇒ compounded quarterly

∵ After 13 years, the balance reaches $19,280.02

∴ A = 19,280.02

∴ t = 13

Substitute these values in the rule above to find P

∵

∴

→ Divide both sides by

∴ 7,821.99888 = P

→ Round it to the nearest dollar

∴ 7,822 = P

∴ P = $7,822

∴ The initial amount of investment was $7,822.

it costs $20 to interview each person for a survey. find the cost to obtain a +- 3% margin of error.

step-by-step explanation:

copy and paste, put it in google

4x and 6y

im not sure though