This is a classic algebra problem with 2 equations and 2 unknowns. Let N = #nickles and D=#dimes.
Then N+D=65 the number of coins he has.
Also 5N +10D=490 working the amount of money in pennies. Put equation 1 into 2
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5N+10(65-N)=490
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5N+650-10N=490
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-5N=-160
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N=32 and D=33
To check 32 + 33 = 65
160 + 330 = 490 (in 1c increments)
