number series logical reasoning questions

16.

Look at this series: 80, 10, 70, 15, 60, … What number should come next?
A.     20    B.     25
C.     30    D.     50
Answer & Explanation

Answer: Option A

Explanation:

This is an alternating addition and subtraction series. In the first pattern, 10 is subtracted from each number to arrive at the next. In the second, 5 is added to each number to arrive at the next.
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17.

Look at this series: 2, 6, 18, 54, … What number should come next?
A.     108    B.     148
C.     162    D.     216
Answer & Explanation

Answer: Option C

Explanation:

This is a simple multiplication series. Each number is 3 times more than the previous number.
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18.

Look at this series: 5.2, 4.8, 4.4, 4, … What number should come next?
A.     3    B.     3.3
C.     3.5    D.     3.6
Answer & Explanation

Answer: Option D

Explanation:

In this simple subtraction series, each number decreases by 0.4.
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19.

Look at this series: 8, 6, 9, 23, 87 , … What number should come next?
A.     128    B.     226
C.     324    D.     429
Answer & Explanation

Answer: Option D

Explanation:

8 x 1 – 2 = 6
6 x 2 – 3 = 9
9 x 3 – 4 = 23
23 x 4 – 5 = 87
87 x 5 – 6 = 429 …