For which firm(s) can the amounts raised by them be concluded with certainty in each year?
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Correct answer: B
How each firm behaves. A firm raises Rs. 1 crore in its first and last year, climbs to a single peak, then falls back to 1. Every year-to-year change is , , or crore, and no two neighbouring years are equal. So from a firm's span (first to last year) and its known total we can reconstruct its year-by-year path.
- Drjbna (2011–2015, total 10): the only mountain that fits is . (Fully fixed.)
- Czechy (2013–2017, total 9): only . (Fully fixed.)
- Bzygoo (2012–2015, four years): total forced to 7, but the middle can be or . (Not unique.)
- Alfloo (2009–2016, total 21): two paths that differ only at the peak — 2012/2013 is or ; both give 2014:3, 2015:2, 2016:1. (Not unique.)
- Elavalaki (2010–?, total 13): three possible paths — (ends 2014); ; or (both end 2015). (Not unique.)
Year-by-year table (bold = fixed; a slash lists the alternatives):
| Firm | '09 | '10 | '11 | '12 | '13 | '14 | '15 | '16 | '17 |
|---|---|---|---|---|---|---|---|---|---|
| Alfloo | 1 | 2 | 3 | 4/5 | 5/4 | 3 | 2 | 1 | – |
| Bzygoo | – | – | – | 1 | 2/3 | 3/2 | 1 | – | – |
| Czechy | – | – | – | – | 1 | 2 | 3 | 2 | 1 |
| Drjbna | – | – | 1 | 2 | 4 | 2 | 1 | – | – |
| Elavalaki | – | 1 | 3/2 | 5/3/4 | 3/4/3 | 1/2/2 | –/1/1 | – | – |
This question — which firms are fully pinned down every year?
A firm is certain only if exactly one valid schedule exists. Drjbna () and Czechy () each have a single path. Bzygoo, Alfloo and Elavalaki each allow two or more. So only Czechy and Drjbna are fully determined.
Answer: Only Czechy and Drjbna