Question

Three friends went to a bookshop the first bought 3biros and 4pencils for $30.00, the second bought 2biros and 5pencils for $27.00 and the third bought a biro and a pencil only.How much did pay?

Answer 1

Answer:

9 dollars

Step-by-step explanation:

Let the cost of one biros be x and the cost of one pencil be y .

then , first ⇒ 3x + 4y = 30  → equation 1

          second ⇒ 2x + 5y = 27 → equation 2

let's multiply 2 with equation 1 and 3 with equation 2

Then , equation 1 → 6x + 8y = 60 →equation 3

           equation 2 →6x + 15y = 81 → equation 4

let's subtract equation 3 from equation 4

6x + 15y = 81

- 6x - 8y = 60

          7y = 21

       ⇒ y = 3

Substituting y in equation 2

2x + (5×3 ) = 27 ⇒ 2x + 15 = 27 ⇒ 2x = 12 ⇒ x= 6

also the third person bought one pencil and one biro

∴ the amount he paid = 6 + 3 = 9