Linda put an amount of money into each of two new investments, A and B, that pay simple annual interest....
GMAT Data Sufficiency : (DS) Questions
Linda put an amount of money into each of two new investments, A and B, that pay simple annual interest. If the annual interest rate of investment B is \(1\frac{1}{2}\) times that of investment A, what amount did Linda put into investment A
- The interest for 1 year is \(\$50\) for investment A and \(\$150\) for investment B
- The amount that Linda put into investment B is twice the amount that she put into investment A
Understanding the Question
Let's restate what we're looking for: What specific dollar amount did Linda invest in investment A?
Given Information
- Linda made two investments: A and B
- Both pay simple annual interest
- Investment B's interest rate = 1.5 × Investment A's interest rate
- We need the exact principal amount in investment A
What We Need to Determine
To find a specific dollar amount, we need either:
- The actual interest rate AND the interest earned, OR
- Some other constraint that uniquely determines the principal
Key insight: When a problem gives us relationships between variables but not actual values, it often signals insufficient information.
Analyzing Statement 1
What Statement 1 Tells Us
- Investment A earned \(\$50\) interest in one year
- Investment B earned \(\$150\) interest in one year
Testing Different Scenarios
Let's think about what this reveals. Investment B earned exactly 3× as much interest as A (\(\$150\) vs \(\$50\)). But wait—B's interest rate is only 1.5× A's rate. How can B earn 3× the interest with only 1.5× the rate?
The answer: B must have 2× as much principal invested!
But here's the crucial question: What's the actual interest rate? Let's test two scenarios:
Scenario 1: If A's rate = 5%
- Then A's principal = \(\$50 ÷ 0.05 = \$1,000\)
- Check: \(\$1,000 × 5\% = \$50\) ✓
Scenario 2: If A's rate = 10%
- Then A's principal = \(\$50 ÷ 0.10 = \$500\)
- Check: \(\$500 × 10\% = \$50\) ✓
Different rates give us different principal amounts. We cannot determine the exact amount Linda invested.
Conclusion
Statement 1 alone is NOT sufficient.
This eliminates answer choices A and D.
Analyzing Statement 2
Now let's forget Statement 1 completely and analyze Statement 2 independently.
What Statement 2 Provides
The amount Linda invested in B is twice the amount she invested in A.
Logical Analysis
This gives us a ratio: \(\mathrm{B} = 2\mathrm{A}\). But without knowing:
- The actual dollar amounts
- The interest rates
- The interest earned
We have infinite possibilities. For example, Linda could have invested:
- \(\$1,000\) in A and \(\$2,000\) in B
- \(\$5,000\) in A and \(\$10,000\) in B
- Any amount in A and twice that in B
Conclusion
Statement 2 alone is NOT sufficient.
This eliminates answer choice B.
Combining Both Statements
Combined Information
- From Statement 1, we deduced that B has 2× as much principal as A (because B earned 3× the interest with only 1.5× the rate)
- From Statement 2, we're explicitly told that B = 2A
The Critical Realization
Here's where it gets interesting: Statement 2 just confirms what we already figured out from Statement 1! It doesn't add any new information.
We still have the fundamental constraint from Statement 1:
Principal in A × Rate of A = \(\$50\)
Since we don't know the actual interest rate, this equation has infinite solutions:
- If rate = 1%, principal = \(\$5,000\)
- If rate = 2%, principal = \(\$2,500\)
- If rate = 5%, principal = \(\$1,000\)
- And so on...
Conclusion
Even combining both statements, we cannot determine the exact amount Linda invested in A. The statements together are NOT sufficient.
This eliminates answer choice C.
The Answer: E
The statements together are not sufficient because we still don't know the actual interest rate, leaving us with infinite possible values for the principal amount in investment A.
Answer Choice E: "The statements together are not sufficient."