math ( grade 6 )

review my answers and please tell me if i got them right or wrong and if I get any wrong please explain the answer to me

Donna deposits $275 into her savings account. she leaves the money in her account, untouched, for 6 years. if the account earns 4.5% simple interest each year, how much simple interest will she have earned by the end of the sixth year?
a. $7,425.00-mine
b. $74.25
c. $206.25
d. $12.38

Over the course of 11 years, Lea earned $800 in simple interest on her investment. if the investment has an interest rate of 6% per year, approximately how much did she have in the account initially?
a. $1,212.12
b. $528.00-mine
c. $436.36
d. $1,466.67

Michelle wants to make a long-term investment. She wants to triple an initial investment of $2,000. If she invests at a simple interest rate of 12% per year, approximately how long will it take her to principal to triple?
a. 25 years-mine
b. 33.3 years
c. 16.7 years
d. 8 years

Rae wants to make $5,000 in simple interest over the course of 7 years. She has $8,500 to invest. At what interest rate should she invest to reach her goal?
a. 11.9%
b. 4.1%
c. 8.4%-mine
d. 2.4%

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  1. #1. sorry. Did you do even a simple sanity check? There's no way %275 could earn $7425 in 6 years.
    275(0.045*6) = 74.25

    #2. No way it could have earned that much. What strange formula are you using, or are you just guessing? If guessing, you apparently have no concept of the magnitude of interest growth.
    P(.06*11) = 800
    P = 1212.12

    #3. The amount doesn't really matter.
    1+.12n = 3
    n = 16.7 years

    #4. Finally!
    8500*7r = 5000
    r = 0.084 = 8.4%

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    oobleck
  2. oobleck is right except for number 3, number 3 is 25 years instead of 16.7 years.

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    2. 👎
  3. 1. B (74.25)
    2. A (1,212.12)
    3. A (25 years)
    4. C (8.4%)
    These are the correct answers! Oobleck had 3 correct answers

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