 # All scale drawings must have a scale written on them. Scales are usually expressed as ratios. Normally for maps and buildings the ratio: Drawing length:

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All scale drawings must have a scale written on them. Scales are usually expressed as ratios. Normally for maps and buildings the ratio: Drawing length: Actual length For maps the ratio is normally in the ratio: Map distance: Actual Distance Example: 1cm : 100cm The ratio 1cm:100cm means that for every 1cm on the scale drawing the length will be 100cm in real life Example: 1:10000 The ratio 1:10000 means that the real distance is 10000 times the length of one unit on the map or drawing.

 When a figure is dilated, its size is changed by multiplying the length of each side by a scale factor. All angles remain the same and so the new shape (or image) is similar to the original.  Can be found by dividing a new side length by the original side length. When going from a small shape to a larger shape the scale factor is greater than 1. (Enlargement) When going from a small shape to a larger shape the scale factor is greater than 1. (Enlargement) When going from a large shape to a smaller shape the scale factor is When going from a large shape to a smaller shape the scale factor is less than 1. (Reduction) less than 1. (Reduction) 1. Determine the corresponding side lengths. 2. Determine if you are making a larger shape or a smaller shape. 3. Determine if the scale factor is greater than or less than 1. 4. Write the correct ratio.

Scale factor = new measurement old measurement -Scale factor more than 1 => shape gets bigger (Enlargement) - Scale factor less than 1 => shape gets smaller (Reduction) - Congruent shapes are similar shapes with SF = 1 Old measurement x SF = new measurement SF new old

 The scale can be written as a scale factor, which is the ratio of the length or size of the drawing or model to the length of the corresponding side or part on the actual object.  Scale Factor needs to be the SAME UNITS!

This HO gauge model train is a scale model of a historic train. A scale model is a proportional model of a three-dimensional object. Its dimensions are related to the dimensions of the actual object by a ratio called the scale factor. The scale factor of an HO gauge model train is. 1 87 This means that each dimension of the model is of the corresponding dimension of the actual train. 1 87

Keep like units in the same fraction. Inches = yards Inches yards

 There is more than one way to set up a proportion correctly!  Cross Multiply!  Use common sense!

 Tom is drawing a blueprint for a rectangular shed he wants to build. The scale factor is 1 ft. to ¼ inch. If the dimensions of the blueprint are 1 ¼ in. by 2 inches, what are the actual dimensions of the shed going to be?

¾ inch to 1 foot  If the length in inches is 2 ¼ inch, what would the actual length be in feet ?

a/8 and 2/4

# 12 page  1cm: 30 km  2.3 cm : ___ km

Practice Pages 226 and 227  #1-17 odd only

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