Free Mensa IQ Number Series Completion Practice Test

Question 1

What is the next number? 3, 7, 13, 21, 31, ?

Accepted Answer

B. 43

Answer

Differences: 4, 6, 8, 10, 12 — increasing by 2 each time. Next difference = 12, so 31 + 12 = 43.

Question 2

Complete the series: 2, 3, 5, 8, 13, 21, ?

Accepted Answer

C. 34

Answer

This is the Fibonacci sequence — each number is the sum of the two preceding ones: 13+21=34.

Question 3

Find the missing number: 1, 8, 27, 64, 125, ?

Accepted Answer

C. 216

Answer

These are perfect cubes: 1³, 2³, 3³, 4³, 5³. The next is 6³ = 216.

Question 4

What comes next? 100, 91, 83, 76, 70, ?

Accepted Answer

A. 65

Answer

Differences: -9, -8, -7, -6, -5. The decreasing differences reduce by 1 each time. Next difference = -5, so 70 - 5 = 65.

Question 5

Find the next number: 5, 10, 20, 40, 80, ?

Accepted Answer

C. 160

Answer

Each number is doubled: 5×2=10, 10×2=20, 20×2=40, 40×2=80, 80×2=160. This is a geometric sequence with ratio 2.

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