Louise has only 5 cent, 10 cent, and 20 cent coins in her purse. She has 30 coins in total and she has two more 10 cent coins than 5 cent coins. If the total value of her coins is $3.80, how many 10 cent coins does she have?

Question

aum · Answer

Let the number of 5 cent coins be x.
The number of 10 cent coins = x + 2  (because "she has two more 10 cent coins than 5 cent coins.")
Number of 20 cent coins = 30 - x - (x+2) (because "She has 30 coins in total")
Number of 20 cent coins = 30 - 2x - 2 = 28 - 2x

Find the total value for each set of coins.

Value in dollars of "x" five cent coins = 0.05 * x
Value in dollars of (x+2) ten cent coins = 0.10 * (x+2)
Value in dollars of (28-2x) twenty cent coins = 0.20 * (28-2x)

Add all the values, equate it to $3.80 and solve for x.

anonymous · Answer

it says the answer is 10 but i do not know how to get it

dumbcow · Answer

you can simplify it by getting rid of decimals  (multiply equation by 100)

--> 5x + 10(x+2) + 20(28-2x) = 380

anonymous · Answer

okay i got that #dumbcow but i get 8

anonymous · Answer

@dumbcow

dumbcow · Answer

good job , x=8

read over aum's post and you will see that "x" is number of 5-cent pieces
what represents number of 10-cent pieces?

anonymous · Answer

how/where do i substitute the x=8 @dumbcow

dumbcow · Answer

number pf 10-cent coins = x+2

"she has two more 10 cent coins than 5 cent coins"
we know she has 8 5-cent coins ...