Multiple choice

Which term of the following series is 1/128? 4, 2, 1, ……

  1. 7th

  2. 8th

  3. 9th

  4. 10th

  5. 11th
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This is a geometric progression with a = 4 and r = 1/2. The n-th term is a * r^(n-1) = 4 * (1/2)^(n-1) = 2^2 * 2^(1-n) = 2^(3-n). Setting 2^(3-n) = 1/128 = 2^(-7) gives 3-n = -7, so n = 10.

AI explanation

The series is a geometric progression with the first term 4 and a common ratio of 0.5. Using the formula for the nth term of a geometric progression, we set 4 multiplied by 0.5 raised to the power of n minus 1 equal to 1/128. This simplifies to 0.5 raised to the power of n minus 2 equaling 1/128, which means n minus 2 equals 7, so n is 10.

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