Final answer:
The number of nickels is 4. Therefore, the correct answer is a. 4 nickels.
Step-by-step explanation:
Let's use variables to represent the number of nickels and dimes.
Let n = number of nickels
Let d = number of dimes
We know that d = 2n - 1, as the number of dimes is 1 less than twice the number of nickels.
Next, let's find the value of the coins. A nickel is worth $0.05 and a dime is worth $0.10.
The total value of the nickels is 0.05n and the total value of the dimes is 0.10d.
We are given that the total value of the coins is $0.90.
So we have the equation: 0.05n + 0.10d = 0.90
Simplifying this equation, we get: 0.05n + 0.10(2n - 1) = 0.90
Expanding and combining like terms, we get: 0.05n + 0.20n - 0.10 = 0.90
Simplifying further, we get: 0.25n - 0.10 = 0.90
Adding 0.10 to both sides, we get: 0.25n = 1.00
Dividing both sides by 0.25, we get: n = 4
Therefore, the number of nickels is 4, so the correct answer is a. 4 nickels.