Quantitative Aptitude

Number Series

2,662 Questions
All First differences and arithmetic progressions 812 Successive multiplication or division 429 Step-wise calculations 349 Squares and cubes based 338 Separate alternate positions 241 Inter-term operations 144 Mixed-operation rules 138 Unconventional pattern solving 74 Fractional and decimal operations 60 Prime number based 54 Digit operations 23

Number Series Questions

Multiple choice

What is the sum of first 6 terms of the series 64, -32, 16 ...?

  1. 22

  2. 32

  3. 42

  4. 52

  5. 86
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This is a geometric progression with a = 64 and r = -1/2. The sum of the first n terms is S_n = a(1 - r^n) / (1 - r). For n = 6, S_6 = 64(1 - (-1/2)^6) / (1 - (-1/2)) = 64(1 - 1/64) / (3/2) = 64(63/64) * (2/3) = 63 * 2/3 = 42.

Multiple choice

Find the number of terms in the series 1/81, - 1/27, 1/9, ….., 729.

  1. 9

  2. 11

  3. 15

  4. 17
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This is a geometric progression with a = 1/81 and r = -3. The n-th term is a * r^(n-1) = 729. (1/81) * (-3)^(n-1) = 729. (-3)^(n-1) = 729 * 81 = 3^6 * 3^4 = 3^10. Since the term is positive, n-1 must be even. (-3)^10 = 3^10. n-1 = 10, so n = 11.