# Thread: do i add the 25% then * it by 306?

1. ## do i add the 25% then * it by 306?

1. An instrument store gives a 10% discount to all students off the original cost of an instrument. During a back to school sale an additional 15% is taken off the discounted price. Julie, a student at the local high school, purchases a flute for $306. How much did it originally cost? A.$325
B. $375 C.$400
D. $408 E.$425

2. Originally Posted by lambofgod
1. An instrument store gives a 10% discount to all students off the original cost of an instrument. During a back to school sale an additional 15% is taken off the discounted price. Julie, a student at the local high school, purchases a flute for $306. How much did it originally cost? A.$325
B. $375 C.$400
D. $408 E.$425
No, you wouldn't do 25% because the last 15% is 15% of the 90% of the original. In mathematical terms:

T(x) = T(0)(1-0.1)(1-0.15) where T(x) is the discounted price and T(0) is the original price. (1-0.1) is the original 10% off and (1-0.15) is the further 15% off

We know T(x) = 306 and need to find T(0)

$T(0) = \frac{306}{(1-0.1)(1-0.15)} = 400$

3. okay im sorta lost, how did you get T(x) = T(0)(1-0.1)(1-0.15) ?

i thought it said since the original discount was 10% and they added another 15% which = 25%

then i was taught to do something like .25*306=

then you get the sum of .25*306 and add it together. any easier way to do this? i cant use the calculator while taking this asvab

4. Originally Posted by lambofgod
okay im sorta lost, how did you get T(x) = T(0)(1-0.1)(1-0.15) ?

i thought it said since the original discount was 10% and they added another 15% which = 25%

then i was taught to do something like .25*306=

then you get the sum of .25*306 and add it together. any easier way to do this? i cant use the calculator while taking this asvab
The only way you could add the 15% and the 10% is if they were both off the original price. As the 15% is not off the original price but rather the original discount which means the 15% is off 90% of the original price.