SOLUTION: Maggie, Amy, and Karen are relatives. They have lived a total of 105 years combined. Maggie’s age is 25 years less than three times Karen’s age. Amy’s age is twice the sum o

Since the Amy’s age is twice the sum of Maggie and Karen’s ages, 

we conclude that the sum of M and K ages is one third of 105, i.e. 35 years,

and the Amy's age is 35*2 = 70 years.



Next, we have

    M + K = 35,     (1)

    M = 3K - 25     (2)


So, we substitute (2) into (1) by replacing M there, and we get one single equation then

    (3K - 25) + K = 35,

    4K = 35 + 25

    4K = 60


which has the solution  K = 15.