Question: What is an 'independent quantity'? EASY!! Multiple choice?

Here's a queston I ran into while working:

Charlie buys three energy bars for each day of his three-day hike. Depending on the brand, the cost of each bar is between \$3.25 and \$4.50. What is the independent quantity?

a) the number of energy bars purchased
b)the total cost of the bars
c) the price of each energy bar
d) the type of hiking shoes Charlie wears

Relation Questions:

a) the number of energy bars purchased

Independent means it is not connected to the rest of the info and quantity is the amount.

You know he will but 3 bars for each of 3 days - so he will buy 9 in total. This won't change.

The total cost can vary from 9 x \$3.25 to 9 x \$4.50 so is not independent as it can change depending on which bars you purchase.

Same for the price, you could spend between \$3.25 and \$4.50 on each one.

The boots themselves won't change unless he takes spares but this is not a quantity and has been put in to throw you i'm guessing. Seeing as this is most likely a math question.