Answer:
a) 20%
b) 50%
c) -75%
Step-by-step explanation:
Mathematically, percentage change is;
(new value -old value)/old value * 100%
(i) (90-75)/75 * 100%
= 15/75 * 100% = 20%
ii) (60-40)/40 * 100%
= 20/40 * 100% = 50%
iii) (5-20)/20 * 100% = -15/20 * 100% = -75%