perimeter and variables

[hansbar]

Parrellagram PRST, PR=ST
Perimeter of PRST is 10 more than 5(RS). If PR=26, find RS.
Mom solves by assigning side PR =x, and RS=Y
2 x and 2y = perimeter
10 +5y=perimeter
2x+2y=10 +5y x or PR=26
2 (26) +2y=10+5y
52+2y=10+5y
42+2y=5y
42=3y
14=y

My daughter says this is not the proper way to solve this with algebra, can you help explain this algebraically

 

[galactus]

I don't know ablut your parallelogram, but I hope this is in the ballpark.

The perimeter is \(\displaystyle 2x+2y=5y+10\)

\(\displaystyle x=26\)

Sub in our equation:

\(\displaystyle 2(26)+2y=5y+10\)

Solve for y.

See what you get?.

y=14

Score one for 'Maw'

Assuming I am interpreting this correctly. I think I am.