Explanation:
well, yes, of course 7 is wrong.
please read the description one more time, slowly and focused.
2 8/9 (or rounded 3) CUPS of mix for 1 (ONE) batch of muffins.
now she wants to make 21 1/2 (or rounded 22, not 21) BATCHES.
you understand ? the 3 is for cups for one batch, and the 22 is for batches (not for cups).
so, when you suddenly divide these two numbers, you actually compare apples and oranges ...
so, let's really think.
1 batch : 3 cups
22 batches : how many cups ?
do you see now what pieces of information are related ?
1 and 22. not 3 and 22.
but what we need to do now is multiply 3 cups by 22, so that the ratio cups to batches stays the same also for 22 batches.
so,
3×22 = 66
she will need approximately 66 cups of mix.