Degrees of Separation to Find Population

Algebra Level 3

It has been calculated that any two random Facebook users are connected by about 4.74 friends, on average (as of 2012). It is quite intimate. On a more inclusive scale, that is, every person on earth, is theoretically connected by approximately 6.6 friends ... "Six Degrees of Separation".

But our goal today has not to do with calculating the degrees of separation, but rather the population of a small boarding school based on such information. In this school, every student knows every other byway of 2.3 2.3 friends (giving the word "friend" a loose definition). The average student has 10 10 friends. What we need to know is the population of the student body.

Expressed in a formula, it looks like this: ln x ln 10 = 2.3 \frac { \ln { x } }{ \ln { 10 } } =2.3

Find the population and round to the nearest whole number. We don't want a fraction of a person.


The answer is 200.

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1 solution

Wwt Manahan
May 15, 2015

ln ( x ) ln ( 10 ) = 2.3 \frac{\ln{\left( x \right)}}{\ln{\left( 10 \right)}} = 2.3 Multiply both sides by ln ( 10 ) \ln{\left( 10 \right)} : ln ( x ) = 2.3 ln ( 10 ) \ln{\left( x \right)}= 2.3\ln{\left( 10 \right)} Take e e to the power of both sides: x = e 2.3 ln ( 10 ) x = e^{2.3\ln{\left( 10 \right)}} Rewrite the exponent: x = e ln ( 10 ) 2.3 x = e^{\ln{\left( 10 \right)}\cdot2.3} Use Product of Powers property in reverse: x = e ln ( 10 ) 2.3 x = {e^{\ln{\left( 10 \right)}}}^{2.3} Use the definition of a logarithm: x = 1 0 2.3 x = 10^{2.3} Rewrite as fractions: x = 1 0 23 10 x = 10^{\frac{23}{10}} Rewrite the exponent: x = 1 0 1 10 23 x = 10^{\frac{1}{10} \cdot 23} Use Product of Powers property in reverse: x = 1 0 1 10 23 x = {10^{\frac{1}{10}}}^{23} Use the fact that a fractional exponent is the same as a root: x = 10 10 23 x = {\sqrt[10]{10}}^{23} Use the calculator or any other method you prefer to find this as a decimal approximation 199.526231496 199.526231496\cdots . Rounding to the nearest person to avoid saying something gory makes 200 200 people.

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