I am confused on this. Please explain it. Thank you!
2 Answers

4 and 10 are corresponding sides. The answer is not simply 4/10. When there are corresponding sides in a ratio problem like this, you square the answer. The answer, therefore, is 16/100 or 4/25.

Area is measured in units squared, so the ratio of their surface area is 4^2 : 10^2 = 16 : 100 = 4 : 25.