Let's use variables to represent the number of nickels and quarters Chelsey has.
Let x be the number of nickels that Chelsey has, and let y be the number of quarters that she has. From the problem statement, we know that:
x + y = 18 (Chelsey has 18 coins in total)
0.05x + 0.25y = 2.10 (the total value of her coins is $2.10)
We can use these equations to solve for x and y.
First, we can solve for x in terms of y from the first equation:
x = 18 - y
Substituting this expression for x into the second equation, we get:
0.05(18 - y) + 0.25y = 2.10
Simplifying this equation, we get:
0.9 - 0.05y + 0.25y = 2.10
0.2y = 1.2
y=6
So Chelsey has 6 quarters. Substituting this value of y back into the first equation, we get:
x + 6 = 18
x = 12
So Chelsey has 12 nickels.
Now we can move on to Alex's coins. We know that he has 1.5 times the number of nickels that Chelsey has, which is:
1.5 * 12 = 18
And he has 2/3 of the number of quarters that Chelsey has, which is:
2/3 * 6 = 4
Therefore, Alex has 18 nickels and 4 quarters.
The dollar value of Alex's coins is:
0.05(18) + 0.25(4) = 0.90 + 1.00 = $1.90
So the dollar value of Alex's coins is $1.90.