# Planet IQ 6: Try this IQ test

Which number should come next in the series?

1 – 1 – 2 – 3 – 5 – 8 – 13

a) 19

b) 21

c) 34

d) 41

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The right answer is b) 21

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How? – Our sequence is:

1 – 1 – 2 – 3 – 5 – 8 – 13

The above series is also known as Fibonacci sequence, where every number after the first two is the sum of the two previous numbers. Here the first two numbers are 1 and 1.

1 – 1 – 2 – 3 – 5 – 8 – 13 so you calculate it like the following

1 – 1 – (1 + 1) – (1 + 2) – (2 + 3) – (3 + 5) – (5 + 8) – (8 + 13) and so on ……

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The Fibonacci sequence is also sometimes expressed with an initial 0. In this case, the first two numbers are 0 and 1.

0 – 1 – 1 – 2 – 3 – 5 – 8 – 13

0 – 1 – (0 + 1) – (1 + 1) – (1 + 2)- (2 + 3) – (3 + 5) – (5 + 8) – (8 + 13) and so on …..

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So the Fibonacci sequence continues

1 – 1 – 2 – 3 – 5 – 8 – 13 – 21 – 34 – 55 – 89 ……….

or

0 – 1 – 1 – 2 – 3 – 5 – 8 – 13 – 21 – 34 – 55 – 89 ……….

Have fun guys 🙂

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