Question

Compound interest rate increases by 20% to 6% what was the starting interest rate

Answer 1

let's reword that

some value "x" increased by 20% and it ended up at 6, the hell is "x" anyway?

well, the value was really "x", oddly enough is the 100%, and if we increase it by 20%, that makes it 100% + 20% = 120%, and we know that is 6, hmmmm

`\begin{array}{ccll} Amount&\%\\ \cline{1-2} x & 100\\ 6& 120 \end{array} \implies \cfrac{x}{6}~~=~~\cfrac{100}{120} \implies \cfrac{ x }{ 6 } ~~=~~ \cfrac{ 5 }{ 6 }\implies x=5`