Hi,
I had this doubt pertaining to combining inequalities.
If we have 2 inequalities with the same 'sign' , can we combine them by addition or subtraction ?
Consider a "remixed" OG problem ( to avoid copyright issues )
If 2p < 2a < 2q and 2r < 2b < 2t is a < b ?
(I) p < r
(II) q < r
if we look at (I) logically we know that even though p < r we cannot assume q < r hence this statement is INSUFFICIENT
looking at (II) we know that if q < r and r < b then it follows that a < b therefore (II) alone is SUFFICIENT.
But if i were to try solving this by combining inequalities :-
(I) p < r
p < a
subtract
0 < r - a
=> a < r
also r < b
adding the two
a + r < b + r
=> a < b hence sufficient
(II) q < r
r < b
add
q + r < r + b
=> q < b
but a < q
adding the two
a + q < b + q
hence a < b therefore sufficient
where am i going wrong with this approach ?
Thanks