First we will find the 11th term
an = a1 + (n-1) * d
a11 = 12 + (11 - 1) * 5
a11 = 12 + 10 * 5
a11 = 12 + 50
a11 = 62
now we use the sum formula...
Sn = (n (a1 + an)) / 2
S11 = (11 (12 + 62)) / 2
S11 = (11 (74)) / 2
S11 = 814/2
S11 = 407
20
U have to divide it by 3 the ratio is 1:3
The individual-size box of cereal is a rectangular prism with a volume of 44.625 inches³.
<h3>What is the volume of a rectangular prism?</h3>
The volume of rectangular prism of length l, width w and height h is given by:
V = lwh.
In this problem, the standard dimensions are:
- l = 3(1/2) = 3 + 0.5 = 3.5 inches.
- w = 8(1/2) = 8 + 0.5 = 8.5 inches.
The individual-size box has a 1/10 of the volume of the original box, hence:
V = 0.1 x 3.5 x 8.5 x 15 = 44.625 inches³.
More can be learned about the volume of a rectangular prism at brainly.com/question/17223528
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