Joe's donut express earned $4,378 at a festival by selling chocolate or vanilla donuts for $2 each if they sold 978 chocolate donuts how many vanilla donuts did they sell

The first thing you should do is calculate the money earned by selling the chocolate donuts. We have then:
 chocolate = (2) * (978) = 1956 $.
 To know the amount of vanilla donuts sold you must first calculate the gain in vanilla donuts by subtracting the total gain with the gain of the chocolate
donuts:
 vanilla = (4378) - (1956) = 2422 $
 The amount of vanilla donuts at $ 2 per donut is:
 # vanilla donuts = (2422) / (2) = 1211
 answer
 they sold 1211 vanilla donut

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