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← JEE Main 2022 · 27 Jun · Shift 2
MathematicsInteger+4 / -1Question 21 of 90

JEE Main 2022 · 27 Jun · Shift 2, Mathematics question 21

Let S={1,2,3,4,5,6,7,8,9,10}S=\{1,2,3,4,5,6,7,8,9,10\}. Define f:S→Sf:S\to S as
f(n)={2n,if n=1,2,3,4,52n−11,if n=6,7,8,9,10f(n)=\begin{cases}2n, & \text{if } n=1,2,3,4,5\\2n-11, & \text{if } n=6,7,8,9,10\end{cases}
Let g:S→Sg:S\to S be a function such that f∘g(n)={n+1,if n is oddn−1,if n is evenf\circ g(n)=\begin{cases}n+1, & \text{if } n \text{ is odd}\\n-1, & \text{if } n \text{ is even}\end{cases}.

Then g(10)(g(1)+g(2)+g(3)+g(4)+g(5))g(10)\left(g(1)+g(2)+g(3)+g(4)+g(5)\right) is equal to ______.

Answer and worked solution

Official answer: 190

Values of f. f=2,4,6,8,10,1,3,5,7,9f=2,4,6,8,10,1,3,5,7,9 for n=1,…,10n=1,\dots,10.

Find g. f(g(n))f(g(n)) is n+1n+1 (odd nn) or n−1n-1 (even nn): g(1)=1g(1)=1, g(2)=6g(2)=6, g(3)=2g(3)=2, g(4)=7g(4)=7, g(5)=3g(5)=3, g(10)=10g(10)=10.

Value. 10(1+6+2+7+3)=19010(1+6+2+7+3)=190.

Answer: 190