If apples are 25 cent's, watermelon is 4 dollars, and cantaloupe is 50 cents . what 25 fruits can I buy with 25 dollars ??

a+w+c = 25

25a+400w+50c <= 2500

You will get a range of fruits.

Or, just start with

6 watermelons cost $24
so, what can you buy with the other dollar? Not enough to make up 25 fruits.

So, consider 5 watermelons for $20
Now you have $5 for the other 20 fruits.

and so on