The solution is that both offers are equivalent, namely a 16,67% discount.

EXPLANATION

Offer 1
(3/18)*100= 16,6666...% = 16,67%(rounded off).

In fact 3 divided by 18 gives the "fraction", i.d.
the ratio (or relation) between the two numbers (itself just a number).
Then muplitplying that ratio (3/18) by 100 gives us the percentage we were looking for.

In other words, when we want to know "how 3 relates with 18"
we in fact ask what is "3" out of "18"?
Mathematically this is expressed by 3/8 which in turn is = 0,16666...
Adding the "%" sign means arithmetically that we multiplied that number (0,16666...) hundred times
This is done to help us. To give us more "sensible" numbers (e.g. "16" and "something")
In our daily life decimals are not at all used.
If you notice; we say "one" dollar AND "fifty" (often omitting the "cents" word)
and not "one point fifty dollars".

Offer 2

The same is valid for the numbers 10 and 60.