If 2 $ 2 = 16 and 3 $ 3 = 36, what is 4 $ 4?
- (a)48
- (b)64
- (c)72
- (d)80
Answer
Why
Correct — B.
Rule: a $ b = (a + b)².
Check: 2 $ 2 = (2 + 2)² = 4² = 16 ✓
Check: 3 $ 3 = (3 + 3)² = 6² = 36 ✓
Apply: 4 $ 4 = (4 + 4)² = 8² = 64 → option (b).
Why the others are wrong
- (a)48 — 48 is 4 × 4 × 3, a multiplier of 3. The examples multiply by 4: 2 × 2 × 4 = 16 and 3 × 3 × 4 = 36, so 4 × 4 × 4 = 64.
- (c)72 — 72 doubles the previous answer, 36. The examples do not double: 16 × 2 = 32, not 36.
- (d)80 — 80 is 4 × 4 × 5, a multiplier of 5. Both examples use 4 (2 × 2 × 4 = 16), which gives 64.
Concept
When both numbers are equal, several rules give the same results: (a + b)², 4ab and (2a)² all produce 16, 36 and 64 here. That is why the item has one answer even though you cannot tell which formula the setter meant.
The quickest reading is the square of the sum: 2 + 2 = 4 → 16, 3 + 3 = 6 → 36, 4 + 4 = 8 → 64.
The results 16, 36, 64 are the squares of 4, 6 and 8. Spotting that the given answers are perfect squares gets you there without naming a formula.
Key facts
- 16 = 4², 36 = 6², 64 = 8².
- With equal numbers, (a + b)² = 4a² = 4ab, so all three rules agree.
- 4 $ 4 = (4 + 4)² = 64.
Study next
Common traps
- Continuing 16, 36 by doubling to 72
- Guessing a multiplier other than 4, which both lines use (2 × 2 × 4 and 3 × 3 × 4)
12 Sep 2025, 12:30, Reasoning Q.20 uses unequal numbers with a² + b²: 7 $ 3 = 58, 6 $ 2 = 40, keyed 5 $ 1 = 26.
23 Sep 2025, 16:00, Reasoning Q.17 cubes the difference: 5 $ 2 = 27, 7 $ 3 = 64, keyed 6 $ 4 = 8.
Related PYQs
No directly related past PYQ was found.