Mary is 1/6 the age of her mother this year. Next year she will be 1/5 the age of her mother. In how many years will she be 1/3 her mother's age.

If mary is x and mother is y,

y = 6x
y+1 = 5(x+1)
so, Mary is 4 and Mother is 24

Now we ask when
24+n = 3(4+n)
n=6

So, in 6 years, Mary will be 10, and Mother will be 30