Find the total marks with and without the absent boy.<br><br>&bull; Total marks of 29 pupils = 79 × 29 = 2291<br>&bull; Total marks of all 30 pupils = 2291 + 90 = 2381<br>&bull; New average = 2381 ÷ 30 = 79.3666...<br>&bull; Correct to 2 decimal places: 79.37<br><br>Final Answer: 79.37