Mary's age is twice her brother's age and half her sister's age. How old is Mary, in years, if the sum of the three ages is 28 years?

ayo crypto

Let Mary's  age  = M

Her brother's age =  M/2

Her sister's age = 2M

So

M    + M/2   +  2M    = 28               simplify

3.5M =  28       divide both sides by  3.5

M =  8     ( Mary is  eight years old )