If n^th term of an A.P. is 6n - 15, then its common difference is :

1. 6

2. -6

3. 12

4. -12

If a : b = b : c, then a : c is equal to :

1. b : a

2. b² : a²

3. a² : b²

4. b : c

A kite shaped card-board is rotated about its line of symmetry (shown by dotted line). The solid figure so obtained has :

(i) one cone formed

(ii) two cones formed

(iii) three cones formed

1. only (ii)

2. only (iii)

3. both (i) and (iii)

4. neither (i) nor (iii)