Sandy gets 3 marks for each correct sum and loses 2 marks for each incorrect sum. Sandy attempts 30 sums and obtains 45 marks. How many sums did Sandy get correct? Pick:	A) 18	B) 21	C) 24	D) 27	E) 28
Let x be the correct sums and (30-x) be the incorrect sums.   3x - 2(30-x) = 45   5x = 105   x = 21   The answer is 21.
<result>B</result>
Sandy gets 3 marks for each correct sum and loses 2 marks for each incorrect sum. Sandy attempts 30 sums and obtains 45 marks. How many sums did Sandy get correct?