 
 <translate> If the 1st fastest dog is 10 years old, and the 2nd fastest dog is 2 years younger than the first fastest dog, the 2nd fastest dog is 10 - 2 = 8 years old. The 3rd fastest dog being 4 years older than the 2nd fastest dog, is 8 + 4 = 12 years old. The 4th fastest dog is half the age of the 3rd fastest dog, meaning the 4th fastest dog is 1 / 2 * 12 = 6 years old. The 5th fastest dog is 20 years older than the 4th fastest dog, meaning the 5th fastest dog is 6 + 20 = 26 years old. The total age of the 1st and 5th fastest dogs is 26 + 10 = 36 years. The average age of the 1st and 5th fastest dogs is 36 / 2 = 18 years old.
The answer: 18. <ibo> Ọ bụrụ na nkịta nke mbụ kachasị ọsọ bụ 10 afọ, na nkịta nke abụọ kachasị ọsọ bụ 2 afọ karịa nkịta mbụ kachasị ọsọ, nkịta nke abụọ kachasị ọsọ bụ 10 - 2 = 8 afọ. Nkịta nke atọ kachasị ọsọ bụ 4 afọ karịa nkịta nke abụọ kachasị ọsọ, bụ 8 + 4 = 12 afọ. Nkịta nke anọ kachasị ọsọ bụ ọkara afọ nke nkịta nke atọ kachasị ọsọ, nke pụtara na nkịta nke anọ kachasị ọsọ bụ 1 / 2 * 12 = 6 afọ. Nkịta nke ise kachasị ọsọ bụ afọ 20 okenye karịa nkịta nke anọ kachasị ọsọ, nke pụtara na nkịta nke ise kachasị ọsọ bụ 6 + 20 = 26 afọ. Ngụkọta afọ ndụ nke nkịta nke mbụ na nke ise kachasị ọsọ bụ 26 + 10 = afọ 36. Nkezi afọ ndụ nke nkịta nke mbụ na nke ise kachasị ọsọ bụ 36 / 2 = afọ 18. Azịza ya bụ: 18. 