Hi, in this session will be learning about alligation now what really is alligation well alligation is a method of finding the ratio in which two or more ingredients should be mixed in order to make a mixture of a desired proportion so we’re mixing two or more quantities alligation is a process mixing it in a desired ratio in order to obtain a particular proportion Let us see with this example in what ratio should you mix two varieties of tea powder one costing 10 per kg and other costing 25 per kg, so as to get a mixture at an average price of 15 per kg now if you realize the difference between the weighted average and alligations is that in weighted average you are given the weights or the ratio in which two ingredient should be added and you are supposed to find the average where is in this case they have given you the average price and you are supposed to find the ratio in which it should be mixed so let’s go back to the lever that we learnt in weighted average so we have to lever and at the end point with the two values 10 and 25 in this case the only difference is we know the average so the balancing point of the lever is known that is 15 per kg so what is the difference from this average from each of the two values as you can see it is 5 from other end and 10 from this end which means the ratio of the differences is 1:2 to 5:10 which is 1:2 and as you know the ratio of the mixing should be reversed right which means the ratio in which these two quantities should be mixed must be 2:1 right and that’s your answer which means alligation and weighted average are two sides of the same coin it’s just that what we need to find and what is given is reverse so what will do is will learn alligation using a slightly different method which is just the modification of this method right for that