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Problem 1:
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Formula: I = prt, Total Amount = p + I
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Work & Solution:
- Principal (p) = $2,000
- Rate (r) = 5% = 0.05
- Time (t) = 8 years
- Interest (I) = 2000 * 0.05 * 8 = $800
- Total Amount = 2000 + 800 = $2,800
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Problem 2:
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Formula: I = prt → p = I / (rt)
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Work & Solution:
- Interest (I) = $400
- Rate (r) = 6% = 0.06
- Time (t) = 3 years
- Principal (p) = 400 / (0.06 * 3) = 400 / 0.18 ≈ $2,222.22
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Problem 3:
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Formula: I = prt
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Work & Solution:
- Principal (p) = $1,800
- Rate (r) = 2% = 0.02
- Time (t) = 3 years
- Interest (I) = 1800 * 0.02 * 3 = $108
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Problem 4:
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a. Peter used the rate as 0.8 instead of 0.08 (8%).
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b. Correct amount of interest:
- I = 275 * 0.08 * 12 = $264
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Problem 5:
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a. Isabella added the principal ($3,000) to the calculated interest ($3,720) to get $6,720, but her calculation of interest is wrong. The correct interest is $720, so the total should be $3,720.
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b. Correct amount of interest:
- I = 3000 * 0.04 * 6 = $720
Parent Tip: Review the logic above to help your child master the concept of simple interest worksheet 7th grade.
