Tammy must give Qiulian 800 cards, so that they have the same number of card.
Given the following data:
Translating the word problem into an algebraic expression, we have;
Qiulian and Tammy have 2400 cards:
[tex]Q+T=2400[/tex] .....equation 1.
Tammy has twice as many cards as Qiulian:
[tex]T=2Q[/tex] .....equation 2.
To determine the amount of card that Tammy must give Qiulian so that they have the same number of card:
Substituting eqn. 2 into eqn. 1, we have:
[tex]Q+2Q=2400\\\\3Q=2400\\\\Q=\frac{2400}{3}[/tex]
Q = 800 cards.
For Tammy:
[tex]T =2Q\\\\T=2\times 800[/tex]
T = 1600 cards.
Therefore, Tammy must give Qiulian 800 cards, so that they have the same number of card.
Read more on word problems here: brainly.com/question/13170908