Pick the equation in each round that does not belong with the other three.

Exercise and reference answers

Questions

1. Items

   1. x² + y² = 25
   2. y = 2x + 3
   3. 2x − 3y + 8 = 0
   4. x + y − 4 = 0

   Reason

   The first three are first-degree equations (straight lines). x² + y² = 25 is a circle.

   Odd item

   x² + y² = 25

2. Items

   1. (4/3) π r³
   2. 4 π r²
   3. π r² h
   4. (1/3) π r² h

   Reason

   The first three involve volume or surface-area of round solids. 4 π r² is the only SURFACE area; the other two are volumes... wait the question is about the odd one.

   Odd item

   4 π r²

3. Items

   1. Cube
   2. Cuboid
   3. Cone
   4. Prism

   Reason

   Cubes, cuboids and prisms have polygonal bases. A cone has a circular base.

   Odd item

   Cone

Explanation