Subtracting m and cm When might you need to subtract lengths?


If you had a piece of ribbon measuring 3m 47cm, and you cut off 1m 75cm to wrap a present, how would you fi nd out how much ribbon you had left? You would subtract the shorter length from the longer length. This is how:


First:


Rename 1m as 100cm and subtract centimetres


2


m 3


– 1 1


cm 47 75


72


Now try these: 1.


a) m cm 4


89 – 1 44 2.


a) 3m 27cm – 1m 84cm


b) m cm 3


71 – 2 21


b) 6m 22cm – 4m 61cm


Then: Subtract the metres 2


m 3


– 1 1


1


cm 47 75


72


c) m cm 3


31 – 1 40


c) 9m 54cm – 1m 67cm


3.


or or 23m 47cm


1


– 1m 75 cm 1m 72cm


2 1 347cm


– 175cm 172cm


= 1m 72cm


d) m cm 5


67 – 1 98


e) m cm 2


56 – 1 89


a) 3m 14cm – 1m 72cm = b) 5m 63cm – 173cm = c) 964cm – 1m 99cm =


Puzzler: Can You Help Jimmy the Giant?


Discuss with friends and at home if you like: you have the rest of the week to try to work this out.


Poor Jimmy the Giant can’t fi nd a bed big enough for him and he fi nds it very diffi cult to get a good night’s sleep on the hard fl oor. Jimmy is 9m 62cm tall and 2m 90cm wide. One day Jimmy has a brainwave. He decides to go out and buy lots of human-size mattresses to put together on the fl oor to make one giant mattress. The mattresses are each 200cm long and 140cm wide. What is the fewest number of mattresses Jimmy will need to make a rectangular-shaped bed that is big enough for him?


Tip: Draw a picture. 76 Length


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