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There are three classes 7th, 8th, and 9th. If the difference between the average marks of class 7th, 8th and 8th, 9th is 90, then what will be the difference of marks between class 7th and 9th?

There are three classes 7th, 8th, and 9th. If the difference between the average marks of class 7th, 8th and 8th, 9th is 90, then what will be the difference of marks between class 7th and 9th? Correct Answer 180

As we know average = Sum of all the observations/Total number of observations

Average marks of classes 7th and 8th – Average marks of classes 8th and 9th = 90

⇒ – = 90

⇒ – = 90 × 2

⇒ 7th – 9th = 180

∴ Required difference = 180

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