If 18, persons can build a 140m long wall in 42 days, the number of days that 30 persons will take to complete a similar 100m long wall is :

(1) 18

(2) 21

(3) 24

(4) 28

A sphere and a cube have equal surface areas. The ratio of the volume of the sphere to that of the cube is

(I) ãƒÎ   : ã6

(2)  2    : ã ƒÎ

(3) ã ƒÎ :  3

(4) ã 6  : ã ƒÎ

If (a - b) is 6 more than (c + d), and (a + b) is 3 less than (c - d); then (a - c) is

1)  0.5 .

2)  1.0

3)  1.5 .

4)  2.0