you'll have to solve simultaneously
let nickel be x, dime be y
x + y = 35 ... ( 1 )
5x + 10 y = 250
5 ( x + 2y ) = 250
x + 2y = 50 ... ( 2 )
in ( 1 )
x = 35 - y ( 3 )
sub ( 3 ) into ( 2 )
( 35 - y ) + 2y = 50
y = 15
sub y into ( 1 )
x + y = 35
x + 15 = 35
x = 20
therefore, Sandy has 20 nickels and 15 dimes
