WillBillDillPickle

15*15 = 225

15-9 = 6

6 * 15 / 2 = 45

225 - 45 = 180 

y intercept = (0, 5)

x intercept = (5/2, 0)

79 - 68 = 11

Yes.

5n + 3f = 15.5 (1)

4n + 4f = 14 (2)

(1) * 4 = (4)

(2) * 3 = (3)

Then we get:

12n + 12n = 42 (3)

20n + 12f = 62 (4)

Subtract

8n = 20

n = 5/2 

4(5/2) + 4f = 14

10 + 4f = 14

4f = 4

f = 1 

The cost of one noteboook and one folder will be 5/2 + 1 = $3.50 

Call the original  number of students, S...and the number of girls  = .60S

Total students  after 20 boys arrive = S + 20

Also:

Number of  girls divided by total number of students  =  58%

.6S  / ( S + 20 )  =   .58    multiply both sides by  S +  20

.6S  = .58( S + 20 )

.6S  = .58S + 11.6   subtract  .58S from  both sides

.02S = 11.6   divide both sides  by .02

S  = 11.6 / .02 =    580

So...the total number of students = 580 + 20  = 600 

B 

2*5 = 10

1.75 * 2 * 1/2 = 1.75

(8-6.75)2 * 1/2 = 8 - 6.75 = 1.25

10 + 1.75 + 1.25 = 13

120,000(1.2)^15 = 1848842.589   Wow, thats alot!

@CPhill. Oops, I calculated the slope wrong.

Formula: 

y = a(1 + r)^x

1.)

2000(1 + 0.04)^3 = 2249.728 = $2249.73

2.)

2000(1.04)^18 = 4051.633031...

3.)

2000(1.04)^6 = 2530.638037... So 6.

4.) I think you already answered it.