Advertisement - Members don't see this ad
Mr. Rostov invested a sum of money into an index fund that pays 9% interest per year. After 30 years, his gain was $1,326,767.85. Prior to the investment, Mr. Rostov was saving $50 per day from his salary. How long did he have to save to invest the needed amount to obtain those gains?
A) 2.5 years
B) 5.5 years
C) 3.5 years
D) 4.5 years
E) 1.5 years
Answer: B
First, determine how much money Mr. Rostov initially invested.
Using the compound interest formula:
A = P(1 + r)ᵗ
1,326,767.85 = P(1.09)³⁰
P = 100,000
So Mr. Rostov invested $100,000.
Next, determine how long it took to save $100,000 at $50 per day:
100,000 ÷ 50 = 2,000 days
2,000 ÷ 365 ≈ 5.5 years
Correct answer: B) 5.5 years
If you’re preparing for the DAT or OAT, the Math Destroyer and the full DAT/OAT Destroyer series are designed to strengthen your problem-solving skills with targeted, exam-focused practice.
Learn more about our resources here:
2025 Math Destroyer | 720 DAT & OAT Quantitative Reasoning Questions
2025 DAT Destroyer – High-Yield DAT Study Guide
For additional free help, join our DAT Destroyer Study Group on Facebook. Inside the group you’ll find:
• Dr. Romano’s Free Biology Review (in the Files section)
• Daily math questions posted by our team
• A supportive community of motivated students
We also offer DAT & OAT classes — available both online and in-person at Snug Harbor:
2026 Winter DAT and OAT Classes with Dr. Jim Romano | In Person or Online
