piggy bank consists of nickels and dimes. there are 30 coins worth $1.90, how many nickels and dimes are in the piggy bank
Let the number of nickels be x
Then the number of dimes, using
ONE PART = TOTAL MINUS OTHER PART,
is 30-x.
Value Value
Type Number of of
of of EACH ALL
coin coins coin coins
-------------------------------------------
NICKELS x $0.05 $0.05x
DIMES 30-x $0.10 $0.10(30-x)
-------------------------------------------
TOTALS 30 ----- $1.90
The equation comes from the column on the right
0.05x + 0.10(30-x) = 1.90
Get rid of decimals by multiplying every term by 100
5x + 10(30-x) = 190
5x + 300 - 10x = 190
-5x + 300 = 190
-5x = -110
x = 22 = the number of nickels
The number of dimes is 30-x or 30-22 or 8 dimes.
Checking: 22 nickels is $1.10 and 8 dimes is $0.80
And indeed $1.10+$0.80 = $1.90.
Edwin