LITTLE BIG TRICK

You can do this by applying little big trick 1 divide two equations and cancel the same terms. You should divide the left side of (A) with the left side of (B) and then divide the right side of (A) with the right side of (B) ... 

It is time to use the powerful little big trick 2 when two unknowns, ATi and AT2 in this case, are coimected with an additional relation, (3-4) in this case, use this relation to express one of the unknowns with the help of the relation. In this way you remove the other unknown. You will use (3-4) to write... 

The molar fractions are known - they are the same as the volume fractions in the mixture of two ideal gases 0.79 for N2 and 0.21 for O2. What we do not know, however, is n, the total number of moles of the two gases in the Earth atmosphere today. Given that molecular masses of the two gases are different their mass ratio (w/w) is different from the volume ratio (v/v). We will simplify this problem by using little big trick 4 use 1 mol as a default value when no quantity is given. Ask yourself a question What is the mass of one mole of air And the answer is, It is the mass of 0.79 moles of N2 with a mass of 28.014 g mol and 0.21 moles of O2 with a mass of 31.999 g mol k Translate the last sentence to a formula and calculate the molar mass of air (a somewhat simplified air) ... 

Now we are going to apply the very powerful little big trick 4 When no amount (mass, or number of moles, or concentration) of product is given you express it as a mathematical variable, x, and use algebra to find its value. 

Now you should apply little big trick 5 You reshuffle or slightly re-scale, by multiplication, for example, (A) and (B), and then subtract them to eliminate the same variables. The trick is based on the following approximations ... 

The mitochondrial DNA we are talking about here can be double stranded or separated into single strands. At some lower temperature, typically, -i-4°C, all of the DNA is double stranded. How much of DNA You may use little big trick 3 and write one mole. So 1 mol, or 100%, of the DNA is dsDNA. Since there are no other forms of DNA, besides the double-stranded and single-stranded ones, present in this sample. 

This is yet another application of little big trick 5 Subtract (B) from (A) and cancel the same terms ... 

What do you do when no amount of the substance - kilograms, pounds, moles -is given You use little big trick 3 assume that you started with one mole. 

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