JOMO 7, Short 8
There are two sequences of integers {ai}i=14 and {bi}i=14
If you do as what is shown, if you cancel the ∑ sign, like ∑j=14bj∑j=14aj=biai∀i∈{1,2,3,4} then it will be a Big Mistake !!!.
But for how many ordered pairs of sequences (<ai> , <bi>) such that 1≤a1<a2<a3<a4≤20 1≤b1<b2<b3<b4≤20 is the above said "False" property seen to be "True" ?
∙ This problem is a part of the set Mistakes Give Rise To Problems , and this question appeared in JOMO 's Contest #7 , and was posed by me.