75) An aeroplane takes 1 hour less for a journey of 1200 km., if its speed is increased by 100 km/hr from its usual speed. The usual speed of the aeroplane is

76) What is the volume of a cone having diameter 20 mm and height 30 mm?

77) In a triangle PQR, the angle PQR is a right angle. The angle PRQ is 60 degree and length of side PR is 20. What is the length of side QR?

78) When a tool is set below the centre, the