math paper 12 may june 2016 discussion

hello, i just took it today,anyone remember the question about a 2 litres water tank?

Yep, I got 64 or so for (A), 996 I think for (B) and 92.3% I think for the last part of the question...not quite sure on how correct they are though.

Reply 2

marksman11

OP

hey derray do u remember what is the question for (c) i only remember it loses 10 litres on the first day and 10% more on next day? am i right? or it is 0.1% more on next day?

Reply 3

marksman11

OP

Original post by deryayyy

Yep, I got 64 or so for (A), 996 I think for (B) and 92.3% I think for the last part of the question...not quite sure on how correct they are though.

how do you solve for (b) and (c)?

Reply 4

deryayyy

I used the 2000= a +(n-1)d I don't remember a and d, and for c I did a*r, my r was 1.1 because it was increasing at 10% and then I found out what that percentage was from 2000. What about you? What did you get?

Reply 5

marksman11

OP

Original post by deryayyy

I used the 2000= a +(n-1)d I don't remember a and d, and for c I did a*r, my r was 1.1 because it was increasing at 10% and then I found out what that percentage was from 2000. What about you? What did you get?

for (b), i used Sn=n/2 (2a+(n-1)b) = 2000 because the tank will lose all of its volume on the nth day.
so 4000=n(20+(n-1)2)
4000=20n+2n^2-2n
4000=2n^2+18n
2n^2+18n-4000=0
n^2+9n-2000=0
n= ( -9+sqrt(81-4 x 1 x -2000) ) / 2
n= 40.4 n= 41 days
for (c) V lost =sn=a(r^n-1)/r-1
V lost =Sn=10(1.1^30 -1)/1.1-1
%V left = (2000-Sn)/2000 x 100%
i got 17.8%

Reply 6

anonymousx9

1

Does anyone remember the exact question? Like including the description they gave at top? At least the description? Please post here. I want to read it again.

Reply 7

Shamita

1

Original post by marksman11

for (b), i used Sn=n/2 (2a+(n-1)b) = 2000 because the tank will lose all of its volume on the nth day.
so 4000=n(20+(n-1)2)
4000=20n+2n^2-2n
4000=2n^2+18n
2n^2+18n-4000=0
n^2+9n-2000=0
n= ( -9+sqrt(81-4 x 1 x -2000) ) / 2
n= 40.4 n= 41 days
for (c) V lost =sn=a(r^n-1)/r-1
V lost =Sn=10(1.1^30 -1)/1.1-1
%V left = (2000-Sn)/2000 x 100%
i got 17.8%

I got n=41 as well...thank god...i was scared when i got n as 40.44 and i had to cancel my working and do it again. For the percentage, i got 17.8 too.