Question:
Look at the following pairs of numbers (a, b) which are related by a proportion b= k·a. (5, 20), (6, 24), (7, 28), (8, 32) What is the value of k?
Solution:
Take any of the given points. For example. take the point (a,b) = (5,20) and replace it into the proportion equation

this gives us:

now, solve for k:

then, the correct answer
4