Answer:
The area of the Iris is 4 times greater.
Step-by-step explanation:
Firstly, we have to realize that we cannot solve this problem without knowing the radius of the iris. because from the information given, the radius of the iris could well be the size of the galaxy and contract from width of 4mm to 2mm and we wouldn't know!
The average radius of the iris is 6mm, so we take this value.
Now, initially the width of the iris is 4mm, that means the radius of the pupil is:
Therefore it's area is:
When the iris contracts to 2mm, the radius of the pupil becomes:
Then it's area is :
To find how many times greater this final area is than the initial area, we just divide it by the initial area:
This is 4 times greater than the initial area.