hmm.. maths help again..

last SG · 2007-02-04T11:33:27+00:00

i try and help... but may be wrong as i haven learn this in my sch... First of all, find the time need for the tank to be full... "A tap is turn on and sal...

papercut87 SG

am here back to bug u maths xperts with with another maths question again..

thanks in advance, Wink

mr_sotong SG

tats easy.. i leave it to other forumer to teach u.. Laughing

bryanseb SG

tats easy.. i leave it to other forumer to teach u.. Laughing

papercut87 SG

Confused

fer those who wld bother to help out.. just to double check.. my ans is 280g..

cheers Very Happy

aku1b0d0 SG

tats easy.. i leave it to other forumer to teach u.. Laughing

ChairmanJay SG

chimnology. give me 5min. i recall my throwaway a math skills to apply to this qn.

DailyFreeGames.com SG

I may be wrong, but here's what i think...

90 litres = 90 grams of salt.

It is gaining 2 grams of salt/min (gaining 4 litres/min - losing 3 litres/min)

It will take another 30 mins to fill the tank.

90 + (30 * 2) = 150 grams.

ditzy SG

Yeah, you're wrong alright. Laughing You forgot to take into account that the initial volume had 1g of salt per litre.

DailyFreeGames.com SG

My solution might be acceptable for pri/sec levels, but i don’t think it works for higher levels because the salt levels going in is more concentrated as time goes, so we can’t simply assume it’s gaining 2 gram salt per min as the solution gets more concentrated, when it’s losing the mixture at 3 litres/min, a higher concentration of salt gets leaked out, which is why we can’t assume it to be gaining 2 gram/min, but i guess if pri/sec school, they won’t care so much.

DailyFreeGames.com SG

Aiyah, the 90 litres = 90 grams of salt is the initial volume mah...

ChairmanJay SG

tank got 90g of salt initially.
den tap turns on while drain got turned on too. overall gain 1litres/min
max cap. for tank is 120litres. so it will takes 30mins to fill the tank.

1st min,
IN: 94litres of salt water, 98g of salt
OUT: 91litres of salt water, 94.87234043g of salt.

2nd min,IN: 95litres of salt water, 102.8723404g of salt
OUT: 92litres, 99.6237402g

3rd
IN 96litres, 107.62.....g
OUT 93litres, 104.260....g

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30th min
IN 123litres lol lost count
OUT 120litres lol lost count

carlsonxjd SG

12am:90 litre urine, 90g salt.
it say leakin at 3litre/min, so we assume that the 3 litre/min is all 1g of salt per L?
since there is 30more Litres to make the tank full.
leaking 3L/min, fill 4L/min is as good as filling in 1L/min
in other words is as good as leaking out 3G salt, fill in 8G salt/min.
5G salt gain /min.
30More litres to fill full the tank require 30mins since the replacment rate is 1L/min.
8G-3g*30mins=150 Grams

12.30am: moreover frm the inital it is 90grams ma. and it leak out 3L/min so actually all the initial 90litre urine, 90g salt are drained. and fulled by 2G/L urine.

carlsonxjd SG

-____________-
if really need to count with "well-stir mixture"
and ure in secondary school lvl.
instead of using ontop method muz ownself come out wif a formula lor.

ChairmanJay SG

i know la jc maths.
i got the formula liao. i lazy to write out.

btw i'm not jc yet. so i'm using sec sch method. Laughing

blue_crimson_89 SG

gosh e math.. try writing out the statistics.. may help for similar qns.. the qn’s pretty easy

secretliker SG

Initially, 90 litres = 90 grams salt.

Water with salt conc. 2g/L flows into tank at 4L/min.

Drained at 3L/min.

Thus, 1L of 2g/L is added to the tank per minute.

At the 91th minute, tank should contain 92g salt with 91 litres.

1L gained = 2g salt gained.

Amount of salt when tank full = (120 - 90) X 2 + 90

150g Mr. Green

polarsnake SG

Shocked

Darkness_hacker99 SG

Laughing

MyPillowTalks SG

ok, i in sec 3, and i failed maths but dunno this can help abit or not:

tank capacity: 120 litre
initially->90litres of salt solution & 90g of salt (info 1)

then, 2g of salt/litre is flowing in @ 4litres/minute, thus, 1 minute, there is 4litre or salt solution, and 8g of salt(info2)

after that, some idiot go and on the drainage pipe, then it starts draining the salt solution at 3litres/minute.

how much salt does it contains when it is full?

in 3 minute, 90l+4l&90g+8g then minus the rate @ 3L/minute, that means...

AIYA I DUNNO@LAR!!!! Mad Evil or Very Mad Mad Mad Mad Mad Laughing

hegu SG

this question requires the use of calculus, you can't solve it using the normal rate x time method...uni maths leh!

becos most of you fail to realise that the mixture is well stirred and hence the concentration of salt in the tank is always changing and hence the amount of salt drained out will change every second.