The answer for your math problem is 55.2. To get this, you do 70 times 0.80, which gives us 56. Then, subtract it by 0.80.
Technically this is not necessarily true for all. A function has each input mapped to one output, therefore there can be two inputs that have the same output. However, when inverted, the input will have two outputs, which is not a function. For example with (1,3) (2,3) (3,4) (4,5) this is a function but switched (3,1) (3,2) ! Two inputs have the same output, which is not a function!
Let the regular price be p. Then the new price, after a 35% markdown, is 0.65p.
Mult. $3.29 by 0.65, Result: $2.14. No match here.
Mult. $4.19 by 0.65. Result: $2.72. We've got a match here!
Mult. $2.79 by .65. Result: $1.81. No match here.
Mult. $3.09 by .65. Result: $2.01. Match!
And so on.
