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Brainteasers

Multiplication & division

Example 1

{2, 11, 1, 22, 2, 2, 4, 16, 1, 1, 1, 1}

This sequence involves multiplication.

For every set of four numbers, multiply the first three to get the fourth.


Example 2

Geometric sequences involve multiplying each term with a common ratio, 'r'

The common ratio for a geometric sequence can be derived by dividing any term by the preceding term.

{4.5, -9, 18, -36, 72, -144, ...}

This sequence has a negative common ratio of -2, (r= -2).

1. {960, 480, 240, 120, ?, 30, ?}

Answer: 60 and 15

Explanation: Each number is halved. (common ratio, r = 1/2)



2. {2, 2, 4, 8, 32, 256, ?}

Answer: 32 x 256 = 8192

Explanation: For every set of three numbers multiply the first two in order to get the third number.


3. {360, ?, 180, 60, 15, 3}

Answer: 360/1 = 360

Explanation: The ratios of the consecutive items are 1/1, 1/2, 1/3, 1/4, 1/5..


4. {4, 4/3, 4/9, 4/27, ?}

Answer: 4/81

Explanation: Each term is one third the previous term. (common ratio r, = 1/3).


5. {0.3, 0.6, ?, 2.4, 4.8, 9.6}

Answer: 1.2

Explanation: Geometric progression sequence, with a common ratio of 2.