Question 1104769
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There is no way to know the right answer to ANY problem like this.<br>
You can put any number you want in the blank, and it will as good an answer as any other.<br>
If there is some context in a problem like this that gives us an indication of what kind of sequence this is, then we might be able to find an answer that is PROBABLY  right; but even then we can't be sure.<br>
And as I was typing that and staring at the given numbers, I spotted what the likely pattern is for the given numbers: rotated 180 degrees, the numbers are<br>
 91, 90, 89, 88, (blank), 86<br>
So quite possibly what goes in the blank is the number "87" rotated 180 degrees -- but that does not give us a number....