4pens cost $2.80.
a) how much does 1 pen cost?
b) how much do 3 pens cost?

$0.70/pen; 3 pens for $2.10.

Step-by-step explanation:

(a) Find the unit rate (cost per pen):

$2.80

= $0.70/pen

4 pens

(b) Find the cost of 3 pens.  To do this, mult. the unit rate by 3:

$0.70

* 3 pens = $2.10

   pen

36 girls

step-by-step explanation:

the 48 boys is 4 parts of the ratio

divide 48 by 4 to obtain one part of the ratio

= 12 ← 1 part of the ratio

3 parts = 3 × 12 = 36 ← number of girls

the answer is b: 18

step-by-step explanation:

use the pythagorean theorem to .

a^2+b^2=c^2

plug 18 for "r"

the 2 legs are 18 and 24

18^2+24^2=c^2

324+576=c^2

900=c^2

c=30

30-12=18

18 is the radius

: )