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 + (n-1)d

t2 = 12 and t3 = 24 so d= 24-13=11

so we need to find a1

t2=a1 + (n-1)d

12 = a1 + (2-1)11

12 = a1 +11

1 = a1

then

t15 = 1 + (15-1)11

t15 = 1 + 154

t15 = 155

- math -
**maribel**, Sunday, September 20, 2009 at 8:40pm
use the arithmetic sequence formula

a(n)=a(1)+(n-1)d

last=first+(number-1)difference

?=4+(15-1)20

?=284

im pretty sure lol

## Answer this Question

## Related Questions

- geometry - How many different triangles can be constructed with toothpicks by ...
- Math - Write two algebraic pattern rules for this toothpick pattern. Figure 1 = ...
- Math Problem Solving - in a following pattern, one hexagon takes 5 toothpicks to...
- math - PLEASE HELP ME ANSWER THIS QUESTION. THIS QUESTION IS HARD FOR ME AND i ...
- Math - How do you go from 40,000 to 5,000 in Four steps? Step one: 40000 Step ...
- Algebra - Debbie finished her algebra test early so she decided to check each of...
- Math (firstgrade) - Hello I am Amy.I am in first grade.I am 6 years old.I need ...
- ALGEBRA HELP - When solving the equation, what property was used to go from step...
- geometry - The figure shows some of the steps Jane took to draw a line segment ...
- Quick math help - In which step below does a mistake first appear in simplifying...