A certain distance is covered at a certain speed. If half of this distance is covered in double the time, the ratio of the two speeds is

Two cars are moving with speeds v1 and v2 towards a crossing along two roads. If their distance from the crossing be 40 m and 50 m at an instant of time, then they do not collide, if their speeds are such that 

A box has 100 blue balls, 50 red balls and 50 black balls. 25% of blue balls and 50% of red balls are taken away. Then, percentage of black balls at present is

An article is sold for Rs. 300 at a profit of 20%. Had it been sold for Rs. 235, the loss percentage would have been

The average of the first nine integral multiples of 3 is

The average of nine numbers is 50. The average of the first five numbers is 54 and that of the last three numbers is 52. Then, the sixth number is