Jethalal participated in a weight loss program started at the newly opened…
2024
Jethalal participated in a weight loss program started at the newly opened center named “The Babita Gym”. At the end of every month, the decrease in weight from original weight was measured and noted as 1, 3, 8, 20, 42, … While Jethalal made a steadfast effort, the weighing machine showed an erroneous weight once. What was that?
- A.
3
- B.
8
- C.
20
- D.
42
Attempted by 1 students.
Show answer & explanation
Correct answer: C
In a ‘find the wrong term’ number series, every term after the first is generated from the one before it by a fixed combination of operations — often multiply by a constant and add a value that itself increases in a simple pattern. Once this rule is confirmed on several genuine, uncorrupted consecutive pairs, applying it forward pinpoints exactly which stated term breaks it.
Applying this to the given series 1, 3, 8, 20, 42:
Check the rule between the 1st and 2nd terms: 1 × 2 + 1 = 3, which matches the given 2nd term exactly.
Check the rule between the 2nd and 3rd terms: 3 × 2 + 2 = 8, which again matches exactly — the increment added has risen from 1 to 2.
Apply the same rule from the 3rd term to predict the 4th term: 8 × 2 + 3 = 19. The series states 20 instead, so the rule breaks exactly at this position.
Continue the rule with the corrected value: 19 × 2 + 4 = 42, which matches the 5th (final) stated term exactly — confirming that 19, not 20, is the value the rule actually produces.
Because using 19 in place of 20 makes the very next term line up perfectly with the same rule, the mismatch is confirmed to sit at the 4th position and nowhere else.
The weighing machine's erroneous reading was therefore 20 — the series should have read 1, 3, 8, 19, 42.
