Logs are stacked up in apile as shown in the figure. The top row has 15 logs and the bottom row has 21 logs. How many logs are in the stack?

a1= 1+14=15
an= 7+14=21
s1=(n/2)(a1+an)

(n/2)(15+21) = 18

How do I figure out the n?

Would n be 14?

n/2(26) = 18

26n = 36
n = 36/26

something very wrong with your equation, since n has to a whole number

where does the 18 come from?
you seem to be using the formula
S(n) = n/2(first + last)
so 18 would be the sum of the logs ????
that makes no sense, since the bottom row alone contains 21 logs.

No

To figure out the value of "n" in the equation (n/2)(15+21) = 18, we can solve the equation for "n". Here are the steps to find the value of "n":

1. Start with the equation: (n/2)(15+21) = 18.

2. Simplify the equation by multiplying within the brackets: (n/2)(36) = 18.

3. Divide both sides of the equation by 36 to isolate the variable "n/2": (n/2) = 18/36.

4. Simplify the right side of the equation: (n/2) = 0.5.

5. Multiply both sides of the equation by 2 to get rid of the denominator: n = 0.5 * 2.

6. Calculate the final result: n = 1.

Therefore, the value of "n" in the equation (n/2)(15+21) = 18 is 1.