CHAPTER 12 PROPORTION
RATIO When two quantities are compared in terms of ‘how many times’, it is known as ratio. It is denoted by the symbol ‘:’. E.g. In a class, say, the number of girls : the number of boys= 1:3 means that for every 1 girl, there are 3 boys. Note that two quantities can be compared only if they have the same unit. EQUIVALENT RATIOS When you multiply or divide the numerator and denominator of a ratio by the same number, you get equivalent ratios. PROPORTION When two ratios are equal, they are said to be in proportion. The symbol :: or = is used to denote proportion. E.g. 35:70::2:4 UNITARY METHOD In this method, we first find the value of one unit and then the required value. E.g. If 10 pencils cost Rs. 100, then how much will 40 pencils cost? 10 pencils cost Rs 100. Therefore, 1 pencil costs Rs (100/10)= Rs. 10. Then 40 pencils will cost 10x40= Rs 400.
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