You will save $9
Convert 20% to decimal
Each % is 0.01 so 20×0.01=0.2
Then multiply
45×0.2=9
4(1/2x7)=12 <=> x28/2=12
x=12*2/28=24/28=12/14=6/7
Recall the inverse function theorem: if f(x) has an inverse, and if f(a) = b and a = f⁻¹(b), then
f⁻¹(f(x)) = x ⇒ (f⁻¹)'(f(x)) • f'(x) = 1 ⇒ (f⁻¹)'(f(x)) = 1/f'(x)
⇒ (f⁻¹)'(b) = 1/f'(a)
Let b = 10. Then pick the function f(x) such that f(a) = 10 and f'(a) = -8 for some number a.
