A box of tacks weighs 120 grams when full, when half full it weighs 70 grams. How many grams does the box weigh when empty?

half of the tacks must have a mass of 50 grams. so, I would expect all of the tacks to have a mass of 100g, and the mass of the box would be 20g.

How much does it WEIGH? .02*9.8 Newtons.

120 - 70 = 50

2 * 50 = 100

120 - 100 = ?

To find out how many grams the box weighs when empty, we need to subtract the weight of the tacks from the weight of the box when it's full.

Given:
Weight of the box when full = 120 grams
Weight of the box when half full = 70 grams

First, we need to determine the weight of the tacks. To do this, subtract the weight of the half-full box from the weight of the full box:

Weight of the tacks = Weight of the full box - Weight of the half-full box
Weight of the tacks = 120 grams - 70 grams = 50 grams

So, the tacks weigh 50 grams.

Now, to find the weight of the empty box, subtract the weight of the tacks from the weight of the full box:

Weight of the box when empty = Weight of the full box - Weight of the tacks
Weight of the box when empty = 120 grams - 50 grams = 70 grams

Therefore, the box weighs 70 grams when it is empty.