Question 99394
Let x be the number of nickels. So .05x is the amount of money in nickels and 0.10(x+2) is the amount of money in dimes since there are two more dimes than nickels. Think "number of nickels + 2 = number of dimes. So, .10(x+2) + 0.05x = $1.70.
To make this a lot easier, let's multiply it all by 100 to get rid of the decimal, which we will replace later.

10(x+2) + 5x = 170 That's much better isn't it?
10x + 20 + 5x = 170 Use the distributive property.
15x + 20 = 170  Add your x's
15x = 150  Subtract the 20 from both sides, now divide
x = 10  So there are 10 nickels. 

Now, back to the original form:
0.10(10 + 2) + 0.05(10) = 1.70
0.10(12) + 0.05(10) = 1.70
1.20 + .50 = 1.70.