<PRE><B>Question 554385</B>
Let
Mary has x number of Nickels
Mary has 30-x number of Dimes


Given
Sum of the coins = 2.40 * 100 (Convert $ into cents) 
Sum of the coins = 240


Nickels+Dimes=Sum of the coins
5*(x)+10*(30-x)=240
5x+300-10x=240
-5x=240-300
-5x=-60
-5x/-5=-60/-5
x=12

Nickels = x = 12
Dimes = 30-x=30-12=18



Check
=====
= 12 * 5 + 10*18
= 60+180
= 240 cents
= 240/100 (Convert cents into $)
= $2.40

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