After 20 % of the original number of marbles in a group were removed from the group, 360 marbles remained

Question

After 20 % of the original number of marbles in a group were removed from the group, 360 marbles remained in the group. How many marbles were removed from the group?

Accepted Answer

Choice B is correct. It's given that 20 % of the original number of marbles were removed from the group. Let x represent the original number of marbles in the group. It follows that 20 100 x , or 0.20 x , marbles were removed from the group. Therefore, x - 0.20 x marbles remained in the group. It's also given that 360 marbles remained in the group. Thus, x - 0.20 x = 360 , or 0.80 x = 360 . Dividing both sides of this equation by 0.80 yields x = 450 . Substituting 450 for x in the expression 0.20 x yields 0.20 ( 450 ) , or 90 . Therefore, 90 marbles were removed from the group. Choice A is incorrect. This is 20 % of the remaining number of marbles. Choice C is incorrect. This is the original number of marbles, not the number of marbles that were removed. Choice D is incorrect and may result from conceptual or calculation errors.

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