for a random sampling of 64 light bulbs, determine the probability that the mean time to failure will exceed 820 hours, correct to two sinificant figures.
A student sitting at the back bench in a class has difficulty in reading .What could be his defect of vision? Draw ray diagram to illustrate the image formation of the blackboard when he is seated at the back and front seat State two possible causes of this defect explain the method of correction this defect with the help of ray diagram