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MakcuM [25]
3 years ago
12

sally has 20 coins in her piggy bank,all dimes and quarters. The total amount of money is $3.05. How many of each coin does she

have?
Mathematics
2 answers:
leva [86]3 years ago
7 0
x-\ amount\ of\ dimes\\\\y-\ amount\ of\ quarters\\\\
 \left \{ {{x+y=20} \atop {0,1x+0,25y=3,05\ \ |*(-10)}} \right.\\\\
 \left \{ {{x+y=20} \atop {-x-2,5y=-30,5}} \right. \\+-----\\Addition\\\\
-1,5y=-10,5\ \ \ | divide\ by\ -1,5\\\\
y=7\\\\x=13\\\\There\ are\ 7\ quarters\ and\ 13\ dimes.
Dafna11 [192]3 years ago
5 0
Let d = number of dimes, q = number of quarters 

<span>Sally has 20 coins in her piggy bank, so </span>
<span>d + q = 20 </span>

<span>The total amount of money is $3.05. </span>
<span>Use the value of each coin multiplied by its number to get total value </span>
<span>.10d + .25q = 3.05 </span>
<span>multiply everything by 100 to clear the decimal places </span>
<span>10d + 25q = 305 and </span>
<span>d + q = 20 </span>

<span>solve the second equation above in terms of either d or q - lets do d </span>
<span>d = 20 - q </span>
<span>sub that into the first equation </span>
<span>10d + 25q = 305 </span>
<span>10(20 - q) + 25q = 305 </span>
<span>200 - 10q + 25q = 305 </span>
<span>15q = 105 </span>
<span>q = 105/15 = 7 </span>
<span>and from above </span>
<span>d = 20 - q = 20 - 7 = 13 </span>

<span>so, there are 13 dimes and 7 quarters </span>
<span>verify with orig problem </span>
<span>13 + 7 = 20, OK, and $1.30 + $1.75 = $3.05 
</span>
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