Answer :
The rule for the series 18, 18, 36, 12, 3, 15 is to multiply by 2 and then divide by 3 alternately. Applying this rule to the last number, the correct choice for the next number in the series is 'a. Multiply by 2, then divide by 3', resulting in 30 as the next number hence the correct option is a.
The question requires determining the rule that governs the series 18, 18, 36, 12, 3, 15 and then applying that rule to find the next number in the series. To solve this, we need to look at the relationship between consecutive numbers and check which pattern fits from the given options.
However, if we consider only the operations of multiplication and division and assume that the series is alternating between the two, the rule that consistently applies is to multiply by 2, then divide by 3. Thus, if the number is 15, applying the rule, the next operation should be a multiplication by 2, yielding 30 as the next number.
Therefore, the correct choice is a. Multiply by 2, then divide by 3.
