10 points for whoever can explain this...

[cougarblue84]

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Sam carries $800 in his wallet in denominations of $5, $20, and $50 bills. How many $5 bills does he have if the $5 bills are 5 pieces more than the $20 bills, and 10 times that of the $50 bills?

A. 20
B. 30
C. 50
D. 60
E. 100

 

[drgreen]

Set up a chart:

Value of bill, # of bills, total value of that bill type

let x represent the number of 20$ bills.

5,(x+5),(5)(x+5)
20,x,(20x)
50,((x+5)/10),(5x+25)

We know the total of all the green values is our total in the wallet (800$)

so...

800=(5x+25)+(20x)+(5x+25)
x=25

since there are 25 20$ bills, there are 30 5$ bills,

the answer is choice B

 

[oohchki]

5(10x) + 20(10x-5) + 50(x) = 800
50x + 200x - 100 + 50x = 800
300x = 900
x=3

3 $50 bills, 30 $5 bills, 25 $20 bills.

Edit: Darn, beaten.

 

[dleodyddlek]

It is always better to set up proper equation to solve the problem but if you're confused or not so confident about this type of question, how about you try to start pluging in numbers?

You have only 5 choices which you can start eliminating to narrow down rather quickly.

I started by pluging in 50 into given condition.

50x5 = 250
45x20 =900 wtf? too much $$ already
5x50 = 250

so the answer should be smaller than 50. From one step of brain work for about 15~20 sec you eliminated 3 choices.

now move to 30

30x5 = 150
25x20 = 500
3x50 = 150
sum = 800
Therefore answer choice is B.

For those who takes longer than others to set up an equation for this type of question, don't give up, you're not doomed :]

 

[arash2663]

Sam carries $800 in his wallet in denominations of $5, $20, and $50 bills. How many $5 bills does he have if the $5 bills are 5 pieces more than the $20 bills, and 10 times that of the $50 bills?

A. 20
B. 30
C. 50
D. 60
E. 100

x=# of $5 Bills
y=# of $20 Bills = x-5
z=# of $50 Bills = x/10
5x + 20y + 50Z =800
5x + 20(x-5) + 50(x/10) = 800
300x = 9000-----------------------> x=30

 

[klutzy1987]

5x+20(x-5)+50(x/10)=800

Solving for X gives us a value of x=30.

Never use trial and error unless you have no idea how to do the problem and you finished all other problems. It is way to time consuming.