ITPEC IP April 2023 Question 6
There is a series of numbered boxes stacked as shown in the figure below. The operations described in the table below are performed in the sequence of operations 1 through 4. When the operation 4 is completed, which of the following shows the status of the stacked boxes?
Fig.
Table
Explanation
2 on top of 1 — the boxes form a stack: every operation takes boxes from the top and puts its result back on the top.
Top first, the stack starts as 4, 3, 2, 2, 1.
- •Operation 1: take 4 and 3, put 4 + 3 = 7: 7, 2, 2, 1
- •Operation 2: put 3: 3, 7, 2, 2, 1
- •Operation 3: take 3, 7 and 2, put (3 + 7 + 2) ÷ 3 = 4: 4, 2, 1
- •Operation 4: take 4 and 2, put 4 − 2 = 2: 2, 1
Answer (b)
Why not others:
- •(a) 0 — one box; the operations take 2 + 3 + 2 = 7 boxes and add 4, so five boxes become two, not one
- •(c) 4, 2, 1 — the stack after operation 3; operation 4 has not been applied
- •(d) 1, 2, 2, 1 — four boxes, again contradicting the count of two
Key rule: A stack is last in, first out: all takes and puts happen at the top; counting boxes removed and added is a quick check on the final height.
Algorithm and Programming · AI-written, may contain errors
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