contestada

A person has 20 coins, all nickels and dimes, worth one dollar and 40 cents. How many nickels are there?

If n = number of nickels and d = number of dimes, which system of equations represents the problem?

n + d = 20 and n + d = 1.40
n + d = 20 and 5n + 10d = 1.40
n + d = 20 and 5n + 10d = 140