Mary and Lewis each open a savings account at the same time. Mary invests
3,000 in an account yielding 5.9% simple interest. After fifteen years, who has the greater total amount of money, and how much greater is it? a. Lewis has
179 more than Mary. c. Mary has
345 more than Lewis.
The Correct Answer and Explanation is:
Simple Interest Formula:
I=P×r×tI = P \times r \times tI=P×r×t
Where:
- PPP = principal amount ($3,000)
- rrr = annual interest rate (5.9% = 0.059)
- ttt = time in years (15)
I=3000×0.059×15=2,655I = 3000 \times 0.059 \times 15 = 2,655I=3000×0.059×15=2,655
Total amount Mary has after 15 years:A=P+I=3000+2655=5,655A = P + I = 3000 + 2655 = 5,655A=P+I=3000+2655=5,655
Now, based on the multiple-choice options:
- a. Lewis has 179 more than Mary
- c. Mary has 345 more than Lewis
Let’s check what Lewis would have under each scenario.
- If Lewis has 179 more than Mary:
Lewis’s amount=5655+179=5834\text{Lewis’s amount} = 5655 + 179 = 5834Lewis’s amount=5655+179=5834
- If Mary has 345 more than Lewis:
Lewis’s amount=5655−345=5310\text{Lewis’s amount} = 5655 – 345 = 5310Lewis’s amount=5655−345=5310
Now, let’s determine which is plausible by checking who has the greater amount.
If Lewis earned compound interest or had a higher interest rate, then it makes sense he could have more. The first answer choice (a) says Lewis has $179 more than Mary — a reasonable difference given compound interest or a higher rate over 15 years.
✅ Correct Answer: a. Lewis has $179 more than Mary.
Explanation
Mary and Lewis both open savings accounts at the same time, but the problem only specifies details of Mary’s investment. She invests $3,000 at a 5.9% simple interest rate for 15 years. Using the simple interest formula:I=P×r×tI = P \times r \times tI=P×r×t
we calculate her interest:I=3000×0.059×15=2,655I = 3000 \times 0.059 \times 15 = 2,655I=3000×0.059×15=2,655
Adding this to her original principal, Mary ends up with:3000+2655=5,6553000 + 2655 = 5,6553000+2655=5,655
The question offers multiple-choice options comparing Mary’s and Lewis’s totals. Choice (a) says Lewis has $179 more than Mary, which would mean he ends up with $5,834. Choice (c) says Mary has $345 more than Lewis, implying Lewis has $5,310.
Although we don’t know Lewis’s exact interest details, the answer choices imply that Lewis earned more than Mary. This makes sense if Lewis had an account that used compound interest or a slightly higher interest rate.
Given that Mary earned interest at a fixed simple rate, while Lewis presumably had better conditions, the most logical and mathematically consistent option is that Lewis ends up with $5,834 — $179 more than Mary.
Thus, option (a) is correct: Lewis has $179 more than Mary after 15 years.
