Math heeelp!!?

Question

!)The president of II-Carnation class bought 8pesos and 12 pesos worth of different materials for the room decorations. He spent a total of 180 pesos. If he bought 19pieces of materials, how many of each kind did he buy?

2)Jessa has 27 pieces of 10 peso bills and 20 peso bills. If jessa has 460pesos, how many bills of each kind does she have?

3)Ms. Armyo has 35,000 pesos to invest, one part at 5% and another part at 7%. She wants the income from simple invest on the two invesments to reach a total of 2,150pesos. How much should she invest at each rate?

Answer 1

<<<!)The president of II-Carnation class bought 8pesos and 12 pesos worth of different materials for the room decorations. He spent a total of 180 pesos. If he bought 19pieces of materials, how many of each kind did he buy?>>>

12x + 8(19-x) = 180

4x + 152 = 180

4x = 28

x = 7 = number of pieces bought at 12 pesos each

19 - 7 = 12 = number of pieces bought at 8 pesos each

<<<2)Jessa has 27 pieces of 10 peso bills and 20 peso bills. If jessa has 460pesos, how many bills of each kind does she have?>>>

20x + 10(27-x) = 460

10x + 270 = 460

10x = 190

x = 19 = number of 20 peso bills

27 - 19 = 8 = number of 10 peso bills.

<<<3)Ms. Armyo has 35,000 pesos to invest, one part at 5% and another part at 7%. She wants the income from simple invest on the two invesments to reach a total of 2,150pesos. How much should she invest at each rate?>>>

0.07x + 0.05(35,000 - x) = 2,150

0.02x + 1,750 = 2,150

0.02x = 400

x = 20,000 = number of pesos at 7%

35,000 - 20,000 = 15,000 = number of pesos at 5%