Question 117359
Mrs. Gardner went to the market. She purchased some lettuce heads and some tomatoes. There were 12 items purchased. She bought twice as many tomatoes as lettuce heads. 
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Let # of lettuce be "u"; Let # of tomatoes be "t":

EQUATIONS:
u + t = 12
t = 2u
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Substitute to solve for "u":
u + 2u = 12
u = 4 (# of lettuce)
Substitute to solve for "t":
4 + t = 12
t = 8 (# of tomatoes)
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Cheers,
Stan H.