Answer:
she added 11 plus 10 wrong
Step-by-step explanation:
11 plus 10 = 21
The given sequence is
a₁, a₂, ...,

Because the given sequence is an arithmetic progression (AP), the equation satisfied is

where
d = the common difference.
The common difference may be determined as
d = a₂ - a₁
The common difference is the difference between successive terms, therefore
d = a₃ - a₂ = a₄ - a₃, and so on..
The sum of the first n terms is

Example:
For the arithmetic sequence
1,3,5, ...,
the common difference is d= 3 - 1 = 2.
The n-th term is

For example, the 10-term is
a₁₀ = 1 + (10-1)*2 = 19
Th sum of th first 10 terms is
S₁₀ = (10/2)*(1 + 19) = 100
okay lets foces on question 20. 3/20
all you need to do is times the dinominator into 100 so 20x5=100 and now you have to multipy the same number that you multiplyed the first one by so 3x5=15 so the anwer would be 15/100 and to put that in a decimal you need to see the number on top witch is 15 so your real ANWSER IS .15
A positive 3430. because two negatives that are being multiplied by eachother are automatically positive.
The volume is V=399.48 m to the power of three