Amoney collection has $3.00 worth of coins: nickels, dimes, and quarters. the ratio of nickels to dimes to quarters is 3: 2: 1 how many quarters are in the collection?

They provide all the needed data...

n + d + q = $3.00                           (they provide a ratio) 
3:2:1 = $3.00                                 (let's enter the value of each)
3(.05) + 2(.10) + 1(.25)   
.15 + .20 + .25
.60 = is the value of the ratio   
let's divide the $3.00 by the .60 to get 5
let's now multiply the value of 5 to the ratio and solve the question...

3(5): 2(5): 1(5)
15 nickels
10 dimes
5 quarters