Sandy gets 3 marks for each correct sum and loses 2 marks for each incorrect sum. Sandy attempts 30 sums and obtains 55 marks. How many sums did Sandy get correct?  Choose the correct choice from the following answers.
A) 19
B) 21
C) 23
D) 25
E) 27
Let x be the correct sums and (30-x) be the incorrect sums.   3x - 2(30-x) = 55   5x = 115   x = 23   The answer is 23.
<result>C</result>
Sandy gets 3 marks for each correct sum and loses 2 marks for each incorrect sum. Sandy attempts 30 sums and obtains 55 marks. How many sums did Sandy get correct?