Question

A store sells jars of peanut butter that cost p dollars and jars of jelly that cost j dollars. Winston purchased 3 jars of peanut butter and 2 jars of jelly for $11.50. Peter purchased 2 jars of peanut butter and 4 jars of jelly for $13.00. How much does 1 jar of peanut butter cost? A. $2.00 B. $2.50 C. $3.00 D. $3.50

Answer 1

The cost of 1 jar of peanut butter is $2.50 ⇒ answer B

Explanation:

* Lets change the story problem to equations to solve it

- The cost of a jar of peanut butter is p dollars

- The cost of a jar of jelly is j dollars

- Winston purchased 3 jars of peanut butter and 2 jars of jelly for $11.50

- Peter purchased 2 jars of peanut butter and 4 jars of jelly for $13.00

* Lets write the equations

∵ The cost of a jar of peanut butter is p dollars and the cost of a jar

of jelly is j dollars

∵ Winston purchased 3 jars of peanut butter and 2 jars of jelly for $11.50

∴ 3p + 2j = 11.50 ⇒ (1)

∵ Peter purchased 2 jars of peanut butter and 4 jars of jelly for $13.00

∴ 2p + 4j = 13.00 ⇒ (2)

- Lets solve this system of equation by using elimination method

- Multiply equation (1) by -2

∴ -6p - 4j = - 23 ⇒ (3)

- Add equations (2) and (3)

∴ -4p = -10 ⇒ divide both sides by -4

∴ p = 2.5

∵ p is the cost of 1 jar of peanut butter

* The cost of 1 jar of peanut butter is $2.50