Math
posted by Laurie .
Lianne has nineteen coins worth $1.45. Some coins are dimes & the rest are nickels. How many dimes does she have.
I understand the D + N = 19 & the 10D + 5N = 145, but I don't understand how you'd subtract them from each other?

I answered that same question last night
divide the second equation by 5
2d + n = 29, now put the first underneath it
d + n = 19
subtract
d + 0 = 10
so there were 10 dimes, and from the first equation n=9
so there were 9 nickels
check: is 10+9 = 19 ? yes
value: 10 dimes = $1.00
9 nickels = 0.45
totol $1.45 
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