CFAI Text, Economics Reading 13 Question 7 quantity, question, simple

kasinkei

It’s a simple price elasticity of demand question:
Price of X increases from $10 to $12, quantity demanded declines from 30 to 28.
I thought it would be:
(1210)/((12+10)/2)=0.18 for price, and
(2830)/((28+30)/2)=0.068 for demand
which gives price elasticity of demand as 0.068/0.18 = 0.38
The book’s answer is 0.38 so are they missing a ‘’ sign or am I wrong?

mkytz15

sign is important for income elasticity as well