1.

1). 5.1 feet2). 5.2 feet3). 6.2 feet4). 5.4 feet

Answer»

As PER GIVEN -

Average height of 18 boys = 5 feet

Total sum of heights of boys = average height × number of boys

Total sum of heights of boys = 5 × 18

Total sum of heights of boys = 90 feet

Also average height of remaining 12 students = 5.5 feet

Total sum of heights of 12 boys = average height × number of boys

Total sum of heights of 12 boys = 5.5 × 12 = 66

Total sum of heights of 30 boys = 90 + 66 = 156

∴ Average height of 30 boys = 156/30 = 5.2



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