Oscar has twice as many pennies than he has dimes. All together he has $.84. How many dimes and pennies does he have?

Question

I tried to solve this, but I know I did it wrong, because I got a decimal for the amount of dimes. Here's what I did:

P=D*2
(.01)(P)+(.10)(D)=.84
(.01)(D*2)+(.10)(D)=.84
.01D+.02+.10D=.84
.11D+.02=.84
-.02-.02
____________
.11D+ 0 =.82
____ ___
.11 .11

And this is where I stopped because I got the decimal. Could you guys please help?? Thanks.

Answer 1

X Dimes.
2x Pennies.

10*x + 1*2x = 84 Cents.
12x = 84.
X = 7 Dimes.

2x = 2*7 = 14 Pennies.

Answer 2

Hmmm. How did you get through this step?

(.01)(D*2)+(.10)(D)=.84
.01D+.02+.10D=.84

Answer 3

To avoid the decimals:
$1.00 = 100 Cents.
$0.84 = 84 Cents.
0.01 = 1 Cent.