Re: If a and b are odd integers such that a - b > 7, what is the smallest
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18 Aug 2020, 01:48
IMO C
Let look at an integer sequence: x, b, b+1, ... ,a
In which:
- x,a,b are odd.
- a-b >7
We want to have the smallest (a-x), in other words we want the smallest "distance" between a and x. Basically, we want the smallest a and the biggest x
- The smallest a:
a-b > 7
=> Our set will look like this:
b, b+1, b+2, ... , b+7, ... , a
=> The smallest a will be b+8.
Check: b is odd => a=b+8 will be odd => Satisfied
- The biggest x:
x is an even number smaller than b.
=> Our set: x, ..., b-2, b-1, b
=> Biggest x will be b-1
Check: b is odd => x=b-1 will be even => Satisfied.
So, "the smallest possible positive difference between a and an even number less than b" will be:
a-x = (b+8) - (b-1) = 9.