20 of 50 marbles are white so there are 50-20 = 30 red and blue marbles

The number of red marbles and blue marbles is the same, so there are 30/2 = <<30/2=15>>15 of each color

The difference between the number of white marbles and blue marbles is 20-15 = <<20-15=5>>5

Double the difference is 5*2 = <<5*2=10>>10 marbles

10 marbles are removed to leave 50-10 = <<50-10=40>>40 marbles

# Answer

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<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
There are 50 marbles in a box which has a mixture of white, red and blue marbles. There were originally 20 white marbles and an equal number of red and blue marbles. Jack removes a number of marbles equal to double the difference between the number of white marbles and the number of blue marbles. How many marbles are left in the box?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
40
There are 50 marbles in a box which has a mixture of white, red and blue marbles. There were originally 20 white marbles and an equal number of red and blue marbles. Jack removes a number of marbles equal to double the difference between the number of white marbles and the number of blue marbles. How many marbles are left in the box?
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