RAS question
A machine applies the following operations on each number in sequence: Operation 1: Add the position number (1st number gets +1, 2nd gets +2, etc.) Operation 2: If the result is odd, multiply by 2; if even, divide by 2. Input: 4, 7, 2, 9 What is the final output?
Correct answer: (D) 10, 18, 10, 26.
After adding 1 to the first input, 2 to the second, 3 to the third and 4 to the fourth, and then multiplying every odd result by 2, the machine's final output for 4, 7, 2, 9 is 10, 18, 10, 26.
Explanation
In the first operation, add each number's position to it: 4+1=5, 7+2=9, 2+3=5 and 9+4=13. An odd number is not exactly divisible by 2, so 5, 9, 5 and 13 are all odd. The second operation therefore multiplies each result by 2: 5×2=10, 9×2=18, 5×2=10 and 13×2=26. Thus, in the same order, the final output is 10, 18, 10, 26.
Why the other options are wrong
- (A) A leaves the first and third results at 5 after the first operation, instead of multiplying those odd results by 2 to get 10.
- (B) B shows only the results after the first operation: 5, 9, 5 and 13. It does not apply the second operation of multiplying each odd result by 2.
- (C) C incorrectly changes the first and third intermediate results to 3, although adding the position gives 5 in both cases; multiplying each of those results by 2 should then give 10.
Concept
This question tests sequential operations, position-based addition, and an odd-even condition. In RAS reasoning and mental ability, such questions test whether candidates can apply every step in the prescribed order.