If 9 @ 3 = 36 and 6 @ 2 = 16, then 8 @ 2 = ?
- (a)20
- (b)18
- (c)19
- (d)17
Answer
Why
Correct — A. Find one rule that fits both examples, then apply it.
Rule: a @ b = (a + b) × b.
9 @ 3: (9 + 3) × 3 = 12 × 3 = 36, as given
6 @ 2: (6 + 2) × 2 = 8 × 2 = 16, as given
8 @ 2: (8 + 2) × 2 = 10 × 2 = 20
That is option (a).
Why the others are wrong
- (b)18 — 18 is 8 × 2 + 2, the rule a × b + b. Test it on the first example: 9 × 3 + 3 = 30, not 36.
- (c)19 — 19 is one short of the rule's value, (8 + 2) × 2 = 20. With b = 2 the rule always gives an even number, so an odd result cannot come from it.
- (d)17 — 17 is 8 × 2 + 1. The same pattern on the first example gives 9 × 3 + 1 = 28, not 36.
Concept
An operator item hides a formula behind a symbol and shows it only through examples. Test each candidate rule on every example before applying it: a × 4 gives 9 @ 3 = 36 but 6 @ 2 = 24, so it fails.
Here both results are multiples of b: 36 = 12 × 3 and 16 = 8 × 2. The multipliers 12 and 8 are a + b, which gives (a + b) × b, the same as ab + b².
A second rule also fits both examples: (a − b)² gives (9 − 3)² = 36 and (6 − 2)² = 16. For 8 @ 2 it gives (8 − 2)² = 36, which is not among the options.
So the options, not the examples alone, settle the rule as (a + b) × b.
Key facts
- (a + b) × b turns 9 @ 3 into 12 × 3 = 36 and 6 @ 2 into 8 × 2 = 16.
- (a + b) × b is the same as ab + b².
- (a − b)² also fits both examples but gives 36 for 8 @ 2, which no option offers.
Study next
Common traps
- Stopping at a rule that fits the first example alone, such as a × 4, which gives 24 for 6 @ 2.
- Finding (a − b)², reaching 36, and guessing when 36 is not offered, instead of looking for a second rule.
The companion rule (a − b) × b decides Reasoning Q.18 of this shift, where 9 $ 3 = 18 and 8 $ 2 = 12 give 6 $ 4 = 8.
At 12 Sep 2025, 16:00, Reasoning Q.19, 5 @ 3 = 28 and 4 @ 2 = 18 fit a² + b, so 6 @ 4 = 40.
Related PYQs
No directly related past PYQ was found.