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SBI Clerk Mains 31 October 2020 Memory Based Paper

Option 4 : 68.6

**Given:**

Number of students = 30

Average marks = 68; wrong item = 35; correct item = 53

**Formula used:**

Average = sum of all items/ number of items

Correct sum = sum of all the items – wrong item + correct item

**Calculation:**

Average marks of 30 students = 68

Sum of their marks = 68 × 30 = 2040

⇒ Correct sum = 2040 – 35 + 53 = 2058

∴ Correct average of marks = 2058/30 = 68.6

__Alternate Method__

New average = old average + (actual number - wrong number)/total number of items

New average = 68 + (53 - 35)/30 = 68 - 18/30

New average = 68.6

**∴ New average is 68.6.**