Congratulations toSoh Yong Shengfrom
Raffles Institution, Singapore for this excellent
solution.
We have 0 < a < b which means 1/a > 1/b and so 3 + 1/a > 3 + 1/b.
Flipping over the fraction, we will get 1/(3 + 1/a) < 1/(3 + 1/b) and the
inequality remains the same way round when 2 is added. Flipping over again
for the last time we get
1
2+
1
3+
1a
is greater than
1
2+
1
3+
1b
The second part is a further expansion of the first, and in the process of
repeating the above we
know that it involves just one more flipping over of the fraction, thus
1
2+
1
3+
14 + [1/(a)]
is less than the same thing with b in place of a as the inequality would
be
reversed again.
Lastly the continued fractions are expanded all the way down to 100 + 1/a
and 100 + 1/b.
Observe the above process, we can tell that if the last or biggest number is
odd then the continued
fraction with a in it is bigger. If the last or biggest number is even then
the continued fraction with
b in it is bigger. Each successive continued fraction involves one
more 'flipping over' and reverses
the inequality one more time. The following continued fraction is smaller than
the same thing with
b in place of a: