Steve has 4 pens. The values of the pens are $2, $4, $7, and $12. Which of the following could NOT be the total value of any collection of these pens?
I just can't understand the answer. My answer was D because with four given prices, you can't make 21 dollars.
hoice (A): $14 = $12 + $2. Discard choice (A).
Choice (B): $16 = $12 + $4. Discard choice (B).
Choice (C): $17. There does not appear any way to obtain a total of $17. Let's look at the remaining choices to be sure that this choice is the value that cannot be obtained.
Choice (D): $21 = $12 + $7 + $2. Discard choice (D).
Choice (E): $23 = $12 + $7 + $4. Discard choice (E).Now that all 4 incorrect answer choices have been eliminated, we know that choice (C) must be correct.
Am I just not thinking hard enough?