Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
Olympiad workbook
Exam
Olympiad workbook
Subject
IOQM
Chapter
Permutation and Combination

Olympiad workbook · IOQM · Permutation and Combination

For n ∈ ℕ , consider non-negative integer-valued functions f on \...

For n∈Nn \in \mathbb{N}, consider non-negative integer-valued functions ff on {1,2,…,n}\{1,2, \ldots, n\} satisfying f(i)≥f(j)f(i) \geq f(j) for i>ji>j and ∑i=1n(i+f(i))=2023\sum_{i=1}^n(i+f(i))=2023. Choose nn such that ∑i=1nf(i)\sum_{i=1}^n f(i) is the least. How many such functions exist in that case?

Correct answer

15

Step-by-step solution

∵∑i=1n(i+f(i))=2023∑i=1nf(i)=2023−n(n+1)2\begin{aligned} & \because \sum_{i=1}^n(i+f(i))=2023 \\ & \sum_{i=1}^n f(i)=2023-\frac{n(n+1)}{2} \end{aligned} For ∑i=1nf(i)\sum_{i=1}^n f(i) be least, n=63n=63 ∴∑i=1nf(i) least =7\therefore \sum_{i=1}^n f(i) \text { least }=7 Total number of possible functions equal to number of possible partitions of 7.  i.e. 7=1+1+1+1+1+1+1\text { i.e. } \quad 7=1+1+1+1+1+1+1 =1+1+2+3=1+1+2+3 Total number of partitions =15=15 Number of possible functions =15=15
Practice Permutation and Combination on Quantrex Academy →

More from Permutation and Combination

All Permutation and Combination questions Full Permutation and Combination list All Olympiad workbook PYQs