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The first three stages of a pattern are shown below, in which each line segment represents a toothpick. If the pattern continues such that at each successive stage, three toothpicks are added to the previous arrangement, how many toothpicks are necessary to create the arrangement for the 250th stage? [asy] size(150); defaultpen(linewidth(0.7)); void drawSquare(pair A){ draw((A.x + 0.1,A.y)--(A.x + 0.9,A.y)); draw((A.x,A.y + 0.1)--(A.x,A.y + 0.9)); draw((A.x + 1,A.y + 0.1)--(A.x + 1,A.y + 0.9)); draw((A.x + 0.1,A.y + 1)--(A.x + 0.9,A.y + 1)); } int k = 0; for(int i = 1; i <= 3; ++i){ for(int j = 0; j < i; ++j){ drawSquare((k,0)); ++k; } draw((k+0.1,0.5)--(k+0.9,0.5),EndArrow); ++k; } label("$\cdots$",(k,0.5)); [/asy]

 Jan 22, 2015

Best Answer 

 #1
avatar+130536 
+5

So we would have

4 , 7 , 10 , 13 , 16 , 19 , etc.   and the final arrangement (term) is given by

an = a1 + d(n-1)    where an is the final term, a1 is the first term, d is the arithmetic difference between successive terms, and n is the number of terms......so we have

an =  4 + 3(250 - 1)  = 4 + 3(249)  = 751 toothpicks

 

 Jan 22, 2015
 #1
avatar+130536 
+5
Best Answer

So we would have

4 , 7 , 10 , 13 , 16 , 19 , etc.   and the final arrangement (term) is given by

an = a1 + d(n-1)    where an is the final term, a1 is the first term, d is the arithmetic difference between successive terms, and n is the number of terms......so we have

an =  4 + 3(250 - 1)  = 4 + 3(249)  = 751 toothpicks

 

CPhill Jan 22, 2015

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