1Hill, think of a triangle... Modelling gradients as percentages using metre rulers and elastic http://www.ordnancesurvey.co.uk/images/userImages/misc/education/triangle.jpg To develop children's skills in measuring and expressing gradients as percentages, metre rulers were used. A metre ruler laid flat on the ground gives a convenient horizontal distance of 100 units (cms) and another ruler held upright at one end gives a selection of the same units for vertical climb. A length of shirring elastic can be used to link the two rulers for example, a triangle formed in this way with a 100 cm base and 20 cm height has a 20% gradient. This means that a toy car would climb 20 cms vertically for every 100 cms it travels horizontally. 20 units out of every 100 = 20%. Using the same triangle, it is also possible to translate percentages into ratios and vice versa. If the child travels 4 cms along the horizontal ruler with a toy car and then measures up vertically from this point to the elastic slope, the height will be 1 cm. This is a 1: 5 triangle. These ratios can be multiplied e.g.: 8 cms along .......................... 1.6 cms up12 cms along .......................... 2.4 cms up16 cms along .......................... 3.2 cms up100 cms along .......................... 20 cms up (20%)http://www.ordnancesurvey.co.uk/oswebsite/education/teachingresources/mapwork/investigatinggradients.html
