Sunday, March 22, 2009

Maths Journal #1

Dear 3/4,
Here's the first Maths Journal for term 2. Enjoy! Remember that you will get participation points for contribution to the journal. Feel free to comment (do not flame your friends) on your classmates' answers.

Add the first twenty numbers 1 + 2 + 3 + 4 + ... + 20 in two different ways.
Explain your working.

^^ Ms Seow
Posted by at
Labels:

7 comments:

  1. AnonymousMarch 23, 2009 at 2:47 AM

    first, you make two numbers together to make 10 e.g.1/9 [between 1-10]except 5.....
    next,do the same method for [11-20] .
    then add the tens.

    answer :......210!

    ReplyDelete
  2. AnonymousMarch 23, 2009 at 8:19 AM

    the boring old fashioned way: 1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20=210

    group them into odd and even:
    (1+3+5+7+9+11+13+15+17+19)+(2+4+6+8+10+12+14+16+18+20)=210

    ReplyDelete
  3. AnonymousMarch 24, 2009 at 5:33 AM

    1 way-First you must add 1 to 10.You would get 55.Now add 11 to 20.You would get 155.Now add 155 to 55.You would get 210.210 is your answer.

    2 way-First you must add 20 to 11 because we are adding backwards.eg:1+2,2+1.You would get 155.Now you must add 10 to 1.You would get 55.Now you must add 55 to 155.You would get 210.210 is your answer.
    By:A.Logeswaran

    ReplyDelete
  4. AnonymousMarch 24, 2009 at 5:47 AM

    1)First, you make two numbers together to make 10. E.g. 1&9.(Between 1-10 except 5)
    Next, do the same method as 1) from 11-20.
    Then add the tens.

    Answer:210

    ReplyDelete
  5. AnonymousMarch 26, 2009 at 6:16 AM

    My way is 20x9+20+10=210.

    ReplyDelete
  6. Akila vakiniApril 11, 2009 at 4:13 AM

    1)20 multiply by the next number which is 21=420
    Then devide the 420 by 2=210(20x21/2)
    2)Add then first and the last numbers e.g 1+20 and find the number of pairs which is 10
    so, muitiply 21 by 10=210

    ReplyDelete
  7. liang guifangMay 18, 2009 at 11:34 PM

    liang guifang:
    1+2+3+4+5=15 6+7+8+9+10=40 11+12+13+14+15=65
    16+17+18+19+20=90 15+65=80 40+90=130
    90+130=210

    ReplyDelete

Subscribe to: Post Comments (Atom)