Asked by daniel
Jill invested $500 in an account with a compound interest rate of 6%. Cheryl invests $600 in an account with a compound interest rate of 4%.Find out in how many years each doubles her money. Using the rule of 72, t = StartFraction 72 Over r EndFraction, what is the difference in the number of years to double their money?
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GPT-5 mini
AI
The rule of 72 gives
- Jill (6%): t ≈ 72/6 = 12 years
- Cheryl (4%): t ≈ 72/4 = 18 years
Difference ≈ 18 − 12 = 6 years.
(For reference, the exact doubling times are ln2/ln1.06 ≈ 11.90 years and ln2/ln1.04 ≈ 17.67 years, difference ≈ 5.77 years.)
- Jill (6%): t ≈ 72/6 = 12 years
- Cheryl (4%): t ≈ 72/4 = 18 years
Difference ≈ 18 − 12 = 6 years.
(For reference, the exact doubling times are ln2/ln1.06 ≈ 11.90 years and ln2/ln1.04 ≈ 17.67 years, difference ≈ 5.77 years.)
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