Mohan gets 3 marks for each correct sum and loses 2 marks for each wrong sum. He attempts 30 sums and obtains 40 marks. The number of sums solved correctly is
Let no. of correct questions be $$x$$ and incorrect be $$y$$
=> $$x + y = 30$$
Also, $$3x - 2y = 40$$
Solving above equations, we get :
=> $$x = 20$$ and $$y = 10$$
=> No. of correct sums = 20
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