GATE BT 2021 • Q30
NAT • 1 Mark
Section 2: General Biotechnology
Biomolecules, enzyme kinetics
Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
The sum of the infinite geometric series 1 + ⅓ + ⅓3 + ⅓3 +... (rounded off to
one decimal place) is
Step-by-Step Solution & Explanation
### **Step-by-Step Solution & Mathematical Derivation (GATE BT 2021 Q.30)**
**1. Governing Concept & Definition**:
- **Topic**: Engineering Mathematics & Infinite Geometric Series
- The sum $S$ of an infinite geometric progression $a + ar + ar^2 + \dots$ with common ratio $|r| < 1$ is:
$S = \frac{a}{1 - r}$
**2. Detailed Step-by-Step Calculation**:
- **Given Series**:
$S = 1 + \frac{1}{3} + \frac{1}{3^2} + \frac{1}{3^3} + \dots$
- First term $a = 1$
- Common ratio $r = \frac{1}{3} < 1$
- **Sum Evaluation**:
$S = \frac{1}{1 - 1/3} = \frac{1}{2/3} = \frac{3}{2} = 1.5$
**3. Final Answer**:
- **Calculated Value**: **1.5**
- **Official GATE Accepted Range**: **1.5 to 1.5**
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