The average height of 30 boys out of a class of 50, is 160 cm. If the average height of the remaining boys is 165 cm, the average height of the whole class (in cm) is:
In an examination, a student scores 4 marks for every correct answer and loses 1 mark for every wrong answer. If the attempts all 75 questions and secures 125 marks, the number of questions he attempts correctly, is:
20 litres of a mixture contains milk and water in the ratio 5 : 3. If 4 litres of this mixture are replaced by 4 litres of milk, the ratio of milk to water in the new mixture will become:
