Answer:
the constant of proportionality k, is the constant value of the ratio of two proportional quantities y and x
Explanation:
k = y/x or y= kx
example : the cost of 20 books is rs. 180 how much will 15 books cost ?
a. rs. 125
b. rs. 130
c. rs. 135
d. rs. 140
answer is c. rs. 135