Answer
Find out the how many tiles are in each section .
To prove
Let us assume that the number of tiles are in section are be x.
As given
A mosaic at the art museum is divided into 6 sections that each contain about the same number of tiles.
There are 2,889 tiles total in the mosiac .
Than the equation becomes
6 × x = 2889

x = 481.5
Therefore the total number of tiles in each sections are 481.5 .

As

, the sequence

converges to zero.
If you're talking about the infinite series

well we've shown by comparison that this series must also converge because we know any geometric series

will converge as long as

.
1/2 : 1
2 : 4
3 : 6
Notice that every ratio consists of a number and double the number.
For 1/2 cup lemon juice, use 1 cup sugar.
The amount of sugar is twice the amount of lemon juice.
The ratio is 1:2
Since you are told the ratio is 1:r, that means r is 2.
The unit rate is 2 cups sugar per cup of lemon juice.
I mean, I don't know how to explain a generic way to solve this. Ask me about the specific train of thought if you are interested:
7 * 18 + 45 / 3 - 2 = 139