87) A "fire-wall" in a computer system acts as

88) A man is watching from top of a tower a boat speeding away from the tower. The boat makes an angle of depression of 45 degree with the man's eyes when at a distance of 60 meters from the tower. After 5 seconds, the angle of depression becomes 30 degree. Wh

89) The thickness of a light gauge sheet steel can be best checked with a

90) The ratio of number of boys and girls in a school of 720 students is 7:5. How many more girls should be admitted to make the ratio 1:1?

91) Which ofthe following can be used as an Inverter?