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percentage off problem setup issue

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percentage off problem setup issue

by GMatt08 » Mon Mar 10, 2008 9:46 am
Kind of confused on how to set this one up:

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

Thanks for any help y'all can give!

-Matt
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by tmmyc » Mon Mar 10, 2008 10:43 am
This is how I would set up this question.

Set 'x' as the original cost of the instrument.

Julie first gets a 10% discount. This means she only pays 90% of the original cost.

x*.9

Then, Julie gets an additional 15% off the discounted price. She only pays 85% of the discounted price.

(x*.9)*.85

Julie pays $306, so

(x*.9)*.85 = 306

Solve for x.
Last edited by tmmyc on Mon Mar 10, 2008 12:52 pm, edited 1 time in total.
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by smar83 » Mon Mar 10, 2008 10:45 am
That's correct. 400 is the answer.
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by GMatt08 » Mon Mar 10, 2008 11:18 am
Oh that makes so much sense now! Thank you!

I'm so rusty on math but it's starting to come back slowly.

Very appreciated,

-Matt
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by ikant » Mon Mar 10, 2008 7:44 pm
Hello all,

Since you have sen the theory behind sucessive discount problems, I may give you a formula that is very handy to crack these problems.

When two successive discounts are given of a% and b% then the net discount offered = a + b - (a*b)/100

Once you get the net discount percentage, one can easily claculate the price.

Cheers,
iKant
"To do is to be"
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by gmat765 » Thu Apr 17, 2008 7:40 pm
I will go with c, too
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by AleksandrM » Fri Apr 18, 2008 9:26 am
You could also just backsolve. Pick 375 and multiply it by 10%, you get a result with change, which means that there will be change in the answer, which means that it is wrong. Pick 408, same result. Try 400:

400(.10) = 40

400 - 40 = 360

360(.15) = 54

360 - 54 = 306

This all took me under 2 minutes.
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