Lucie must buy 5 more than half of Suzie's purchase to have 10 more cards than two thirds of the girls’ total
Represent Lucie's card with L and Suzie's card with S.
So, the total number of cards is:
Total = L + S
Lucie's number of cards can be represented as:
L = 10 + 1/3(L + S)
Multiply through by 3
3L = 30 + L + S
Subtract L from both sides
2L = 30 + S
Divide by 2
L = 15 + 0.5S
Let x represents the additional number of cards.
So, we have:
x + L = 10 + 2/3(L +S)
Substitute L = 15 + 0.5S
x + 15 + 0.5S = 10 + 2/3(15 + 0.5S + S)
Evaluate the sum
x + 15 + 0.5S = 10 + 2/3(15 + 1.5S)
Expand
x + 15 + 0.5S = 10 + 10 + S
Evaluate the sum
x + 15 + 0.5S = 20 + S
Subtract 0.5S from both sides
x + 15 = 20 + 0.5S
Subtract 15 from both sides
x = 5 + 0.5S
The above means that Lucie must buy 5 more than half of Suzie's purchase to have 10 more cards than two thirds of the girls’ total
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