07/05/07
On today’s class Mr. A told us how he is going to grade the scribe post and he also gave us some tips to make it better. He used Thursday’s scribe as an example and showed us things that could be improve and the post of the evaluation format he is going to use to grade us. Since we were frying in the trailer we moved to the AV-room and there we almost got intoxicated (it smelled horrible). There we did our usual schedule, so we started the POD:
POD
A pile of logs has 30 logs in the bottom row. Each higher row has one log fewer ending with 9 logs in the top row.
How many logs are in the pile?
After some minutes trying, Alex went to the board and showed his way of solving the problem. His method was using Gauss’s Technique;
After Alex’s collaboration, Mr. A told us that they were more ways to solve it. Since no one knew how else to do it he showed us two more ways.
Using the series sequence equation
1. S30-S8
Sn=N/2(n+1)
30/2(31)-8/2(9)
15(31)-4(9)
465-36=429 logs
After we completed the POD, we finished a problem that we started the last class:
Mr. A gave us a new equation:
Sn= n/2(n+1)- Sum of 1st n positive integres
*Sn = n/2(t1+tn) - Sum of 1st n term of an arithmetic series.
We first used it with the POD problem and later we did it with new problems to practice.
30/2(1+30)+8/2(1+8)
Find S25 35+40+45 –Arithmetic series
d=5
t25=t1+(n-1)d
t25 =35+(25-1)5
t25 =35+(24)5
35+120=155
Sn=n/2(t1+tn)
S25=25/2(35+155)=2,375
Find the sum of the frist 30 terms of the arithmetic series
-5+-14+3+7+........
S30=?
Kris showed us her work:
Y = mx+b
-5=4(1)+b
b =-5-4
b =-9
Tn =4n-9
T30 =4(30)-9
T30 =111
S30=30/2(-5+111)
S30=15(106)
S30=1590
Mr.A showed us a shorter way to do it:
tn= t1(n-1)d
t30=-5(29)(4)
t30=111
Another problem: S is arithmetic
S22=? t1= 18 t5 = -2
d= total jump/ number of jump
d= -20/4
d=-5
tn= t1(n-1)d
t22= 18(22-1)-5
t22=-87
S22=22/2(18-87)
S22=-759
There is no new homework, quiz or assignments for today.
We pick Kris to do the next scribe post.
2 comments:
Eli and Dark Angel im sorry I wasnt here last week, but when going over your Scribe I read the solution of the log problem and didnt understand it so much. I am not saying the srcibe was bad or anything its that because I wasnt in class, Im wondering if either of you or someone else can help me with the solution to that problem or what do the variables stand for?
Here is another question. In Kris´solution to -5+-14+3+7+........, looking for S30. What does each term in y=mx+b stand for?, Its that I am confused with Kris´explanation and Mr. A´s
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