Question 86219
7. let x = original price of CD player
a. 25% off: .75x  [after deducting 25%, the price is 75% of what it was initially]
$30 off: x - 30
b. .75x - 30
c. .75(x - 30)
d. .75(150 - 30) = .75(120) = $90
e. because by applying the discount first the initial price is lowered by 25%, then $30 is taken off the lower price. Otherwise, you'd be deducting $30 from the full price instead of from the lowered price, then taking 25% off the reduced price, which is less of a deduction than taking 25% of the full original price.
8a. V(r(t)) = {{{4/3}}}pi*{{{(0.3t)^3}}} = {{{4/3}}}pi*{{{0.027t^3}}} = 0.036pi{{{t^3}}} = {{{9*pi*t^3/250}}}
b. input is t [time] and output is V [volume]
c. V = {{{9*pi*5^3/250}}} = {{{9*pi/2}}}