inequalities & solving equations

Question

sarawong spent half of his weekly allowance on clothes. to earn more money his parents let him wash the dog for 9. what is his weekly allowance if he had ended with 15.

Answer 1

Hi Eli, this is a 'backwards problem.' We'll start from the very end and work our way backwards.

 

 

 

• The problem tells us that Sara Wong ended the week with $15, which is some money he was given + some extra money he earned.

 

• His parents let him wash the dog for $9, which means that before he washed the dog, he has $15 - $9 = $6. This means that he had $6 in his pocket before his parents let him wash the dog for extra money.

 

• The $6 he had before washing the dog was half of the money that his parents gave him in the beginning. That means he spent the other half ($6) on clothes. In order to calculate how much he had in the beginning, we can do the following:

 

 

$6 (spent on clothes) + $6 (left over) = $12 

 

 

• This means that in the beginning, he had a weekly allowance of $12.

Answer 2

Here's what we know:

½a + 9 = 15 (half the allowance plus another 9 is $15)

Subtract 9 from both sides:

½a = 15 - 9

½a = 6

Multiply by 2:

a = 6 * 2

a = 12