SOLUTION: Mary's age is seven-tenths of Mark's age. In 4 years Mary's age will be eight-elevenths of Mark's age. How old is Mark now?

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Question 26020: Mary's age is seven-tenths of Mark's age. In 4 years Mary's age will be eight-elevenths of Mark's age. How old is Mark now?
Answer by Paul(988) About Me  (Show Source):
You can put this solution on YOUR website!
Mary's age = 7x/10 or 0.7x
Mark's age = x
In 4 years mary's age = 4+0.7x
In 4 years mark's age = 4+x
Mary's age = mark's age

%288%28x%2B4%29%29%2F11=0.7x%2B4
%288x%2B32%29%2F11=0.7x%2B4 --_> multipply the whole equation by 11 to remove the fraction:
11%28%288x%2B32%29%2F11%29=11%280.7x%2B4%29
8x%2B32=7.7x%2B44
8x-7.7x=44-32
0.3x=12
x=40
7(40)/10 = 28

Hence, Mary's age is 28, and Mark's age is 40.
Paul.