percentages

percentage point drop

old percentage - new percentage

finding an old value

new value ÷ (1 - percentage)

percent change formula

[(new value - old value) ÷ old value] × 100

total interest

finding the difference: new value - old value

future value

PV × (1 + r)^{n × k}

present value

FV ÷ (1+ r)^{n × k}

when can you add percentages?

when they share the same base.

what does it mean when doing doubles?

it goes up by 100%! (2 - 1 = 1)

what does it mean when something goes up by 100%?

it doubles!

what does it mean when something goes up by 200%?

it triples!

what does it mean when something triples?

it goes up by 200%! (3 - 2 = 3)

what does it mean when something goes up by 1.5?

it goes up by 50%! (1.5 - 1 = .5)

what does it mean when something goes up by 50%?

it goes up by 1.5!

something happening to a rate (e.g., bonus, increase, etc)

"You have a 2% cash-back rate. The bank gives you a 3% bonus on that rate."

2 + (0.03 × 2) = 2.06%