Teacher's Guide - Pearson

Note: It can be pointed out to students that the ratio stays the same since bothareas changed by the same factor.d) Shaded area 5 18 3 20 2 2 3 π 3 4.5 25 232.8 m 2Note: It is important for students to understand that two circles with a diameter of9 metres each do not have the same area as one circle with diameter 18 metres,i.e. 2 3 4.5 2 9 2 .4. a) Shaded area 5 π 3 40 2 2 2 3 π 3 20 25 2 513.3 m 2b) Ratio 5 ​1__ ​ 5 1:1 (i.e. the areas are equal)1c) Perimeter small circles 5 2(2 3 π 3 20)5 251.33 mPerimeter big circle 5 2 3 π 3 405 251.33 mRatio 5 1:1d) Diameters and perimeters double.5. a) ​√ ________(5 2 2 3 2 ) ​ 5 4 cmb) Area 5 ​1__ ​(sum || sides) 3 ⊥height25 ​1__ ​ (18 1 12) 3 425 60 cm 2c) Area 5 3 2 3 60 5 540 cm 2d) Ratio 5 9:16. a) 0.75 mb) Area door 5 3.9 m 2Perimeter door 5 7.9 mArea windowc) ___________ ​ 5 ___ 16​Area door 25 ​ 5 0.64 : 1_______________Perimeter window​ 5 ​4__Perimeter door 5 ​d) Area window 5 2.5 m 2Perimeter window 5 6.3 mChapter 12: Area and perimeter71