Select the option in which the numbers share the same relationship as that shared by the given pair of numbers. (7, 333) (5, 115) (NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding/deleting/multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
- (a)(3, 24)
- (b)(6, 226)
- (c)(8, 492)
- (d)(4, 54)
Answer
Why
Correct — D. Rule: cube the first number, then subtract 10.
7³ = 343, and 343 − 10 = 333
5³ = 125, and 125 − 10 = 115
Apply the same rule to each option's first number:
4³ = 64, and 64 − 10 = 54, which is option (d).
Why the others are wrong
- (a)(3, 24) — (3, 24) subtracts 3, not 10: 3³ = 27 and 27 − 3 = 24.
- (b)(6, 226) — (6, 226) adds 10 instead of subtracting it: 6³ = 216 and 216 + 10 = 226.
- (c)(8, 492) — (8, 492) subtracts 20: 8³ = 512 and 512 − 20 = 492.
Concept
The bracketed note is the instruction that matters. Operate on whole numbers, never on their digits, which closes off reading 333 as 3-3-3 and hunting for a digit pattern.
With that shut, run the standard ladder on the numbers you are given: square, cube, a multiple, then a small constant added or taken away.
333 sits just below 343 and 115 just below 125. Both gaps are 10, and that fixes the rule in a single line.
Every option here is a cube with a small constant attached, so a rough resemblance proves nothing. Cube first, then compare the exact difference.
Key facts
- The given pairs follow n³ − 10, since 7³ − 10 = 333 and 5³ − 10 = 115.
- 4³ = 64, so 4³ − 10 = 54.
- The bracketed note forbids splitting a number into digits before operating on it.
Study next
Common traps
- Accepting a cube-plus-or-minus rule without checking the constant is the same in both given pairs.
- Breaking 333 into its digits, which the note explicitly forbids.
- Testing the rule against one given pair when the second pair is what pins the constant at 10.
The stem, bracketed note included, repeats with different pairs — asked on 17 Sep 2024, 16:00, Reasoning Q.3, on 24 Sep 2024, 12:30, Reasoning Q.9 and Q.17, and on 13 Sep 2024, 16:00, Reasoning Q.15.
Related PYQs
No directly related past PYQ was found.