He has 10 pennies, 13 quarters , 21 dimes and 25 nickels.
Explanation
Suppose, the number of pennies is [tex]x[/tex]
As he has 3 more quarters than pennies, 11 more dimes than pennies and 2.5 times as many nickels as pennies....
So, the number of quarters [tex]= x+3[/tex],
the number of dimes [tex]= x+11[/tex] and
the number of nickels [tex]=2.5x[/tex]
We know, the value of each penny is $0.01 , value of each quarter is $0.25 , value of each dime is $0.10 and value of each nickel is $0.05
Given that, the total value of all coins is $6.70
So the equation will be.....
[tex]0.01x+0.25(x+3)+0.10(x+11)+0.05(2.5x)=6.70\\ \\ 0.01x+0.25x+0.75+0.10x+1.10+0.125x=6.70\\ \\ 0.485x+1.85=6.70\\ \\ 0.485x=6.70-1.85=4.85\\ \\ x=\frac{4.85}{0.485}=10[/tex]
So, the number of pennies is 10 , number of quarters is (10+3)= 13 , number of dimes is (10+11)= 21 and number of nickels is (2.5×10)= 25