A geometric sequence has first term 4 and common ratio 3. What is the sum of its first 4 terms?
Answer and explanation
Correct answer: B. 160
- Step 1: S_n = a_1 (q^n - 1) / (q - 1).
- Step 2: S_4 = 4 x (3^4 - 1) / 2 = 160.
Answer
160.
Why not the others: The other values use one term too many, give a single term, or forget to divide by q - 1.
Practise more Probability, counting and sequences.
Free questions with an explanation for every one, and full timed Tawjihiya Bahrain (Secondary School Certificate) mock tests.
More Probability, counting and sequences questions
- The first term of an arithmetic sequence is -2 and the common difference is 4. What is the 10th term?
- A geometric sequence has first term 3 and common ratio 2. What is the 6th term?
- A club has 6 members. In how many ways can a committee of 2 be chosen?
- The first term of an arithmetic sequence is 3 and the common difference is 2. What is the 15th term?
- 7 runners compete in a race. In how many ways can the first 2 places be awarded?
- The first term of an arithmetic sequence is 5 and the common difference is -3. What is the 10th term?