The three numbers in each group are related in the same way.Choose the number that completes the last group.( 8 [ 12 ] 32 )( 8 [ 16 ] 64 )( 8 [ ? ] 40 )A13B18C8D5E16

The relationship in each group is that the third number is the product of the first two numbers.

In the first group, 8 * 12 = 96, not 32. In the second group, 8 * 16 = 128, not 64. So, the relationship seems to be incorrect based on the given groups.

However, if we assume that the relationship is that the third number is four times the second number (since 32 is four times 8 and 64 is four times 16), then the missing number in the third group should be 10 (since 40 is four times 10).

But 10 is not an option in the given choices (A13, B18, C8, D5, E16). Therefore, there seems to be a mistake in the question or the provided options.

The relationship in the numbers is that the third number is the first number multiplied by the square of the second number.

In the first group (8 [12] 32), 8 * (12/2)^2 = 32.

In the second group (8 [16] 64), 8 * (16/2)^2 = 64.

So, in the third group (8 [?] 40), we need to find a number which when halved, squared, and then multiplied by 8 gives 40.

Let's denote the unknown number as x. So, we have 8 * (x/2)^2 = 40.

Solving this equation for x gives x = sqrt(40/8)*2 = sqrt(5)*2 ≈ 4.47.

However, this number is not in the options.

So, it seems there might be a mistake in the question as none of the options fit the established pattern.