This is one problem I made:
The rectangular lot has a width of 5 cm. If the perimeter is 40 cm, what is the length?
The formula for the perimeter of a rectangle is P=2(L+W)
since P is 40, just substitute:
40=2(L+5)
Divide both sides by 2
20=L+5
Subtract both sides by 5
15=L
The length is 15 cm. If you tried to check it:
P=2(L+W)
P=2(15+5)
P=2(20)
P=40 cm
Hope this helps =)
