A pile of 55 coins, consisting of nickels and dimes, is worth $3.90. find the number of each.

Answer is: 32 nickels and 23 dimes.

x - number of nickels.

y - number of dimes.

two equations in two unknowns:

1) x + y = 55

2) 0,05x + 0,1y = 3,90.

nickel is a five-cent coin.

dime is a ten-cent coin.

solve equation 1) for x and substitute for x in equation 2)

x = 55 - y

0,05 · (55 - y) + 0,1y = 3,90 2,75 - 0,05y + 0,1y = 3,90

0,05y = 1,15

y = 23.

x = 55 - 23 = 32.