Happy hour prices Part-3(revised)

Due to the barkeeper's illiteracy the new price board becomes as follows.

• $\dfrac 12$ L drink $\implies$ $3-2=\$1$ ,
• $1$ L drink $\implies$ $10-4=\$6$ and
• $2$ L drink $\implies$ $20-11=\$9$

So, we can conclude that it is better to buy a $2$ L drink instead of two $1$ L drinks, because, $2×\$6=\$12>\$9$

Also, we find that the $\dfrac 12$ L drink is the cheapest. And as specified we can buy only $10$ such drinks,we order for the specified quantity, i.e. $10×\$1=\$10$ . Hence we get $5$ L.

Now, as we are left with $25-5=20$ L, we order for $10$ , $2$ L drinks which will cost us $10×\$9=\$90$

So, the total cost is $10+90 \\ = \$100$