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In this question there are two rules to follow that are applied alternately.
The first rule is that the colours change - black changes to dark grey, dark grey changes to light grey, light grey changes to white, and white changes to black.
The second rule is that the triangular grid rotates by 120? anticlockwise.
To obtain the next diagram in the sequence, the first rule should be applied, and the correct answer is A.

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In this question the black squares move three places clockwise around the outside of the grid.
The only exception is when a black square lands on the centre square at the top of the grid. In this case, in the next diagram of the sequence, it moves down the centre line of the grid by three places. When it reaches the centre square of the bottom of the grid, it then continues clockwise around the outside of the grid.
The correct answer, therefore, is B.

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In this question there are 5 different sized letter X's. There are two rules to follow that are applied simultaneously.
The first rule is that the X's in the second and third positions (counting from the left) change positions.

The second rule is that the fifth X moves to the first position and the others all move along one position towards the right. These two rules are applied simultaneously.
Following these rules, the missing diagram of the sequence is D.

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In this question there are three balls that move into, around and out of a grid of equilateral triangles.
There are two rules to follow that are applied alternately.

The first rule is that the balls drop down through a horizontal edge of a triangle. If a ball drops down outside the grid, it is lost and doesn't appear in the next diagram of the sequence.

The second rule is that the triangular grid rotates through 120? clockwise.
For the next diagram of the sequence, the first rule should be applied and the correct answer is A.

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In this question there is an equilateral triangle with a bold corner and a regular pentagon with one edge thin-lined. Each shape follows its own rule.
The equilateral triangle rotates by 120? clockwise each time. Following this rule, the correct answer could be B or C.
The regular pentagon rotates by 72? anticlockwise each time.
Following this rule, the correct answer could be C or D.
When both rules are applied simultaneously, therefore, the correct answer must be C.