Posted by molly on Sunday, September 20, 2009 at 8:25pm.
Natasha has to determain the number of toothpicks in the 15th step, step one has four toothpicks step two has 12 toothpicks and step three has 24 toothpicks. She does not want to draw 15 pictures then count the toothpicks. Explain or show how she could do this.

math  sydney, Sunday, September 20, 2009 at 8:34pm
tn = a1 + (n1)d
t2 = 12 and t3 = 24 so d= 2413=11
so we need to find a1
t2=a1 + (n1)d
12 = a1 + (21)11
12 = a1 +11
1 = a1
then
t15 = 1 + (151)11
t15 = 1 + 154
t15 = 155

math  maribel, Sunday, September 20, 2009 at 8:40pm
use the arithmetic sequence formula
a(n)=a(1)+(n1)d
last=first+(number1)difference
?=4+(151)20
?=284
im pretty sure lol
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