Dan is cutting 4.75 foot length of twine from a 240 foot spoil of twine. he needs to cut 42 lengths and says that 40.5 feet of twine will remain. show that this is reasonable

1 length is 4.75 feet

42 lengths = x feet            Cross multiply

1 * x = 42 * 4.75                  Multiply on the right

x = 199.5

amount left = amount started with - amount amount used

Amount left = ???

Amount started with = 240 feet.

Amount used = 199.5               Substitute

Amount left = 240 - 199.5        Subtract

Amount left = 40.5                    Answer