Melody

here is a slightly different way.

I would have multiplied  both sides by 10

10(1/2x + 4/5x) =10*2

5x+8x=20

13x=20

x=20/13

CPhill has the 100 in his equation too Rosala.

he used   r=0.034  and you used r=3.4/100  

see, they are the same.  :)

I think yours was just a careless error.

you had P=1200 instead of P =2200    

I am sorry anon but your answer is not correct.  Can you work our why?

$$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{tan}}^{\!\!\mathtt{-1}}{\left({\mathtt{2}}\right)} = {\mathtt{63.434\: \!948\: \!822\: \!922^{\circ}}}$$

general solution.   Where n is an integer

$$x=(180n+63.43)^0$$

Look at the sticky notes on the right of your page.

Can you be more specific please - I don't understand what you are asking.

this is the second time you have posted this .

Please follow the instructions for reposting.   

I have no idea where to start.

Some of the permutations are obvious but how you would count them I have no idea

I did it exactly the same way - that is comforting for me anyway 

Here is a video on it.

Infinity is not a number TJM

You can not think of it like an ordinary number - it does not work that way.