Both A and B together can complete a work in 20 days and B alone can complete the same work in 36 days. In how many days will A alone complete the work?

Answer: C. 45

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Source: SSC CHSL (Tier-1) 2017 Online Exam Paper held on 15 March 2018, Evening Shift (Quantitative Aptitude) — SSC-published paper with official answer key, via sscportal.in · official-answer-key