GMAT Sentence Correction (SC) | A new skin whitening cream is being sold for four times the

"Than" is used along with a comparative adjective. There is no comparative adjective in the sentence.

X sells for 4 times the price than Y sells .... wrong. (no comparative - hence "than" wrong)
X sells for 4 times the price that Y sells .... correct. ("that" refers to "price" - "that Y sells" is the modifier for "price")
X sells for
...

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