The statemment 3+3=6 serves as a/an to the conjecture that the sum of two odd numbers is an odd number.

The statement 3+3=6 serves as a disproof to the conjecture that the sum of two odd numbers is an odd number.
Odd numbers are numbers which can  NOT be divided evenly into groups of two.
6 can be divided by 2 (6:3=2), which means that the sum of two odd numbers is not an odd number. 
On the other hand, there is a statement that is always true (a theorem) about the sum of two odd numbers: The sum of two consecutive odd numbers is divisible by 4. 

The Ferris wheel rotates 18° between successive cars being at the bottom.

Explanation:

 Angle inside a circle = 360°

 No of cars in a Ferris wheel = 20

 When the bottom of the ride is replaced by the next car, the angle rotated by Ferris wheel is same as the angle between two consecutive cars towards center of Ferris wheel.

  Angle between two consecutive cars of Ferris wheel = 360/20 = 18°

 The Ferris wheel rotates 18° between successive cars being at the bottom.