Brain teaser time?????????

Question

A person bought 25 ballloons.Small ones cost 10 cents abd large ones cost 30 cents.

If the person spent $3.90, how many of each did she buy?

First correct anwser with working out gets the ten points!!!!!!!!!!!!!

Answer 1

18 small- $1.80

7 large- $ 2.10

25- $3.90

Answer 2

$3.90

Answer 3

The number of balloons is 25

so      

x + y = 25

x = 25 - y -------> a

10x + 30y = 390

10 (25-y) + 30y = 390

250 -10y + 30y =390

250 + 20y =390

20y = 140

y = 140/20

y = 7

from a:

x = 25 - y

x = 25 - 7

x = 18

so 18 small and 7 large.

Answer 4

7 large @ 30c = $2.10

18 small @ 10c = $1.80

Total = $3.90

♣

Answer 5

15 small and 8 large   .1s+.3l=3.90

Answer 6

There are 2 possible answers.  The missing variable is the total number of balloons purchased