Answer:
10 ounces
Step-by-step explanation:
The usual size container contains 100% of a mix, then the bonus container contains 120% of a mix.
x ounces - 100%,
12 ounces - 120%,
then
[tex]\dfrac{x}{12}=\dfrac{100}{120},\\ \\x=\dfrac{12\cdot 100}{120}=10\ \text{ounces}.[/tex]