Condensing a Range of numbers.

Hi everyone, I really hope i have posted this is the right section. Maths is not my greatest strength (Itwasntme)

But i find my self in a position needing help, and i have been thinking about this for who knows how long and i can't seem to come up with a formula to solve it.

I am creating a conversion tool for gaming reasons.

At the minute i have a number of mathematical equations that gives me a number in the range of 0-100. My problem now is; i need a way of condensing that number into a range of 50-100....

This is where it becomes confusing for me (Speechless) So i apoligise if it makes no sense, but hopefully it does lol

But a priority is needed, (50 is bad, 75 is good, 80 is great, 90 best, 100 perfect) so if the number in the original range is 49 i can't just condess it to be 75/100, because that would mean it is a good stat. When it is average.... So when condenssing the range of numbers a priority is needed, 0 the worst, 100 the best. So 50-55 would be anything from 0-30 from the original list, 56-60 being 31-49 from the original, then 61-65 / 50-59. 66-70 / 60-70..... Then anything above that i would like to be coverted as it appears in the original....

If it helps i am using Excel to create my converter....

Once again i hope i can get some help :) and i can only apoligise if this is a completely "stupid" question.

Thank You

ja_santacruz