If 4 years are subtracted from the age of a person and divided by 5, the result gives his grandson's age. The grandson now has a sister aged 5, six years younger to him. How old is the grandfather?

Grandson's sister is 6 years younger than grandson and is 5 years old.

From the relationship between the grandson's and sister's ages, we can find the grandson's age. Then, using the equation for the grandfather's age, we solve for x.

Let the grandfather age be x years.

Grandson’s age = 5 + 6 = 11 years

Now, for Grandfather's age:

​$$\frac{x - 4}{5} = 11 \\x − 4 = 55 \\x = 55 + 4 = 59$$​​

Thus, The grandfather is 59 years old.