The light-collecting area of the 10-meter Keck telescope is 4 times greater than the light-collecting area of the 5-meter Hale telescope.
Why?
We can calculate the light-collecting area of a telescope by using its diameter/radius. To do that, we can use the following formula:
![CollectingArea=\pi*((diameter)/(2))^(2) = \pi radius^(2)](https://img.qammunity.org/2020/formulas/physics/high-school/x1geo42knozccq4fss6pgao9xfvo6plao1.png)
Now, to know how much greater is the collecting area of the 10-meter keck telescope compared to the collecting area of the 5-meter hale telescope, we need to calculate their light-collecting areas and compare them.
For the 10-meter keck telescope, we have:
![Keck=\pi *((10m)/(2))^(2)=\pi *(5m)^(2)=25\pi m^(2)](https://img.qammunity.org/2020/formulas/physics/high-school/2ufp1oj0lsdlqyfrg2imq3660osz62gt6j.png)
For the 5-meter hale telescope, we have:
![Keck=\pi *((5m)/(2))^(2)=\pi *(2.5m)^(2)=6.25\pi m^(2)](https://img.qammunity.org/2020/formulas/physics/high-school/g7i077wyr9d5wkd1a8zerl9fego5s47z0a.png)
Now, comparing the areas, we have:
![Ratio=(KecksArea)/(HalesArea)=(25\pi m^(2) )/(6.25\pi m^(2))=4](https://img.qammunity.org/2020/formulas/physics/high-school/745o8hrfos0xdb9ni3ostj1i27s44lr24i.png)
Hence, we have that the light-collecting area of the 10-meter keck telescope is 4 times greater than the light-collecting area of the 5-meter hale telescope.
Have a nice day!