SCALE FACTOR AND SIMILARITY
SCALE FACTOR
A scale drawing of an object is the same shape as the object but a different size.
The scale of a drawing is a comparison of the length used on a drawing to the length it represents. The scale is written as a ratio.
SIMILAR FIGURES
The ratio of two corresponding sides in similar figures is called the scale factor.
Scale factor = \(\frac{length\,in\,image}{corresponding\,length\,in\,object}\)
If one shape can become another using Resizing then the shapes are Similar
Hence, two shapes are Similar when one can become the other after a resize, flip, slide or turn.
(a) A model of a boat is made on the scale of 1:4. The model is 120cm long. The full size of the boat has a width of 60cm. What is the width of the scale model?
(i) 20 cm
(ii) 25 cm
(iii) 15 cm
(iv) 240 cm
(b) What will effect the similarity of any two polygons?
(i) They are flipped horizontally
(ii) They are dilated by a scale factor
(iii) They are translated down
(iv) They are not the mirror image of one another
(c) If two similar triangles have a scale factor of a:b. Which statement regarding the two triangles is true?
(i) The ratio of their perimeters is 3a : b
(ii) Their altitudes have a ratio a:b
(iii) Their medians have a ratio \(\frac{a}{2}\) : b
(iv) Their angle bisectors have a ratio a2 : b2
(d) The shadow of a stick 5m long is 2m. At the same time the shadow of a tree 12.5m high is
(i) 3m
(ii) 3.5m
(iii) 4.5m
(iv) 5m
(e) Below you see a student's mathematical model of a farmhouse roof with measurements. The attic floor, ABCD in the model, is a square. The beams that support the roof are the edges of a rectangular prism, EFGHKLMN. E is the middle of AT, F is the middle of BT, G is the middle of CT, and H is the middle of DT. All the edges of the pyramid in the model have length of 12 m.
What is the length of EF, where EF is one of the horizontal edges of the block?
(i) 24m
(ii) 3m
(iii) 6m
(iv) 10m
