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Mark weighs 74 pounds. Together, he and his sister weigh six more pounds than three times the weight of his sister. What is the weight of marks sister?

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3 Answers

Mark's weight = 74 lb. Mark's sister's weight = w lb. Since Mark and his sister together weigh 6lb. more than thrice the weight of Mark's sister alone, we can write: 74+w = 6+3w To solve this equation for w, first add -w to both sides of the equation. 74+w-w=6+3w-w or, 74 = 6+2w Now add -6 to both sides and simplify: 74-6 = 6+2w-6 or, 68=2w Therefore, w= (68/2) = 34 lb. Always verify if the answer is correct! Marks weight = 74 lb. Marks's sisters's weight = 34 lb. Sum of Mark and his sister's weight = 108 Three time Mark's sister's weight = 3*34 = 102 108 = 102+6 which is the staement of the problem. Final answer: w = 34 lb.

I thought of it similarly to what Robert had answered...translate the words and numbers into math language:

Mark and sister together weigh  74 + S =

Six more pounds than three times sister's weight  3S + 6

Then solve for S (sister's weight)

74 + S = 3S + 6

68 = 2S   (Subtract 6 and S from both sides)

S = 34    ( Divide both sides by 2)

Sister is 34 lbs!

Let W = the weight of Mark's sister.

74+W = 3W+6

Solve for W,

W = 34 lb <==Answer