Answer:
10%
Step-by-step explanation:
Sean first thought that his hand was 20 cm so:
20cm
When he measures with a ruler, he gets 18 cm so:
18cm
The equation is really simple, and you basically do:
20/20 - 18/20 = 2/20 = 1/10 = 10%
The equation is:
1- x/y
x equals the new number
y equals the original number