The average marks obtained by 120 students in an examination is 50. If the average marks of passed students is 70 and average marks of the failed students is 30. then what is the number of students who passed the examination?

60

Let's assume passed student = x

So, failed students are = 120 -x

As per question,

120 x 50 = 70x + (120 - x) x 30

x = 60

So Passed students are 60.