My attempt : Take any $n+1$ integers $1,2,.....,n+1$ , Then there is a pair of integers $1, n+1$ such that :
$$(n+1)-1 = n$$, which is a multiple of n.
My attempt : Take any $n+1$ integers $1,2,.....,n+1$ , Then there is a pair of integers $1, n+1$ such that :
$$(n+1)-1 = n$$, which is a multiple of n.
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Divide each of the $n+1$ numbers by $n$. Since there divisor is $n$ you will get $n$ distinct remainders. But there are $n+1$ numbers hence two numbers will leave the same remainder when divided by $n$. The difference of these two numbers will be divisible by $n$ since their remainders will cancel out.