Solve This
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IF you need to build a pyramid and you start with two cans on top, then 4, then 6, then 8. then 10 and so on and you end up with 1190 cans..how many rows do you have in total?
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298
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u forget u need to add the number of cans as u go along..Originally posted by ditzy:596 -
still wrongOriginally posted by ditzy:298 -
34 haha.
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show the steps pleaseOriginally posted by matleep:34 haha. -
Aiyo.. just use arithmetic progression. secondary school maths
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show lah..did u use quadratic?Originally posted by matleep:Aiyo.. just use arithmetic progression. secondary school maths -
got lah.. lazy to work it out
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No I used MS excel.Originally posted by valentinoo:show lah..did u use quadratic?
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KNN.Originally posted by ditzy:No I used MS excel.
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u use Excel to verify can lahOriginally posted by ditzy:No I used MS excel.
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row 1: 2 cans, total of 2 cans
row 2: 4 cans, total of 6 cans
row 3: 6 cans, total of 12 cans
etc etc
now, lets look at these numbers, and make some ratios here, skipping right to row 2.
so in row 2, we had a total of 6 cans, so if we take the number of rows over the number of cans, we can simplify the fraction: 2(row #)/6(total cans) = 1/3
now, in row 3, we have the total of 12 cans. so lets do that, 3/12 = 1/4
row 4, total of 20 cans, 4/20 = 1/5
and so on.
so lets pick one of these ratio, we can use row 2. 2/6 = 1/3. what can we figure out from here?
row/total cans = 1/row+1
so lets do some math to figure out which row we have 1190 cans in. let X be the row.
X/1190 = 1/X+1
lets do some simple math..
1190(1) = X(X+1)
a little further..
1190 = X^2 + X
0 = X^2 + X - 1190
lets use the quadratic forumula:
where a = 1, b = 1, c = -1190
do some work, and you come out with a 34. -
Wha
. Too deep for me. dun understand -
It is an arithmetic progression. Just work it out.
Sn
=1190
=(n/2)[4+2(n-1)]
=> n=34 -
Originally posted by ditzy:No I used MS excel.
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Wow, boeing767 just pwned the threadstarter.Originally posted by RETARDED_MORON:It is an arithmetic progression. Just work it out.
Sn
=1190
=(n/2)[4+2(n-1)]
=> n=34 -
Why boeing767..?Originally posted by ditzy:Wow, boeing767 just pwned the threadstarter. 
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His other nick in sgforums.Originally posted by d3sT1nY:Why boeing767..? -
Err...the formula is simply:
No. of cans = n(n+1), where n = number of layers. -
its ok..got few ways to do it mah