In true experiments, subjects are put into control and experimental groups using . Group of answer choices 1. Random sampling 2. Random assignment 3. Self-selection 4. Chronological order

To get the best results in an experiment the subjects should be picked randomly.

The answer would be 2. Random assignment.

First, let's figure out what amount of stamps Mark originally had.

1750 - 480 = 1270

Mark originally had 1270 stamps.

Now, we have to figure out how many stamps Lisa has.

s = stamps

1270 + s = (1750 - s)3
1270 + s = 5250 - 3s
Add 3s to both sides.
1270 + 4s = 5250
Subtract 1270 from both sides.
4s = 3980
Divide both sides by 4.
s = 995

Now, subtract 995 from 1750.

1750 - 995 = 755

Lisa now has 755 stamps.