Answer:
Step-by-step explanation:

Answer:
12.57
Step-by-step explanation:
the formula for the area of a circle is 
the diameter is 2 times the radius, so dividing it by 2 gives you a radius of 2
substitute the 2 for the r in the formula and solve

4
≈12.57
Answer:
0.81
Step-by-step explanation:
Answer:
I kinda did a lil of this in my head so i might not be 100% correct, but i would say the bigger group is 20 and the smaller group is 10
Two cheaper books = x
more expensive = 1.5x
so, 2.5x=150
150/2.5=x=60
therefore the more expensive book = 90