math (rate)
posted by Kasie on .
I need help! Ok here's the problem.
Melissa lights 2 candles that are the exact same height at the exact same time. The blue candle takes 6 hours to burn completely. The purple candle takes 9 hours to burn completely. After how many hours will the slower burning candle be twice the height of the faster candle? How tall were the candles originally?
Please help. I'm in 7th grade and normally a very good math student but these are really hard. PLEASE RESPOND QUICKLY! I need this by tomarrow!!!
Bluerate=rb=1candle/6hrs
Purple rate=rp=1candle/9hrs.
Now, the length remaining is the original Length minus the burned part.
Length= Lorig  rburning*Time
Lengthblue= LorigLorig/6*T
When the blue is one half the purple,
length blue= 1/2 Lp
Lorig (1 1/6 T)= 1/2 Lorig(11/9 T)
1T/6= 1/2  T/18
solve for T.
Maria lights two candles of equal length at the same time. One candle takes 6
>hours to burn out and the other takes 9. How much time will pass until the
>slowerburning candle is exactly twice as long as the fasterburning one?
>Explain how you got the answer.
1The faster burning candle, Fb, burns at the rate of L/6 inches per hour.
2The slower burning candle, Sb, burns at the rate of L/9 inches per hour.
3In t hours, Fb burns a distance of tL/6 inches.
4In the same t hours, Fs burns a distance of tL/9 inches.
5The unburned candle lengths at t hours are then (L  tL/6) or (6L  tL)/6 for Fb and (L  tL/9) or (6L  tL)/9 for Sb.
6Since we are looking for the t where Sb's length is twice Fb's length, we can write (9L  tL)/9 = 2(6L  tL)/6.
7Expanding, 54L  6tL = 108L  18tL.
8Eliminating the L's throughout, we have 12t = 54 making t = 4.5 hours.

4.5 hours! It says it doesnt it?! stupid much! Unny way Im sorta a couple years of from when this was due! Im in 7th grade now Ive got a 99 in math1 No im not a nerd, quite the contrary! Im just smart, pretty, and i happen to have alot of freinds, unlike my BF David! JK! Unny way hope u got it rite! Byas!