One gram of a certain health food contains 7 percent of the minimum daily requirement of vitamin E and 3 percent of the minimum daily requirement of vitamin A. If vitamins E and A are to be obtained from no other source, approximately how many grams of the health food must be eaten daily to provide at least the minimum daily requirement of both vitamins?

A. 3
B. 7
C. 10
D. 14
E. 33

Given :  0.07 e + 0.03 a  = 1gm.

Now the least gm to achive the minimum daily requirement of the vitamins can be obtained by increasing Vitamin A to its minimum level of requirement:

i.e. 1 gm of the health food contains ------  ‘0.03*A’ gm of Vit A

So to ensure that minimum req of Vit A is covered we need cover how many gm of health food is required to raise this level to ‘A’ gm

i.e. To cover ‘A’ gm of Vit A  - A/0.03A = 33.33 gm

This many gms of heath-food ensures that it covers the minimum requirement of Vit A and also that of Vit E(actually Vit E would contain additional gms but we don’t care as covering 33.33 gm of the health food ensures that it covers the requirement of both Vit A & E and not of an individual component alone.)

Analogy :

let's say that granola bars come in bulk packs of 7 chocolate chip and 3 oatmeal raisin, and that you can't buy the flavors separately.

you need 100 chocolate chip and 100 oatmeal raisin bars for a catering event.

how many bulk packs do you have to buy?

same deal - you have to buy enough bulk packs to get 100 of BOTH kinds, which means you have to buy 33 1/3 of them (i.e., buy 34 of them) to get enough of the oatmeal raisin kind.
true, you'll have a whole lot of chocolate chip bars just sitting around, but that is irrelevant.