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

A.)n + d = 20 and n + d = 1.40 That's wrong because if n + d = 20, it can't equal 1.40 too!
   
B.)n + d = 20 and 5n + 10d = 1.40 That's wrong because the left side of 5n + 10d = 1.40 is in cents but the right side is in dollars.
 
C.)n + d = 20 and 5n + 10d = 140 That's right, for the left side of 5n + 10d = 140 is in cents and the right side is also in cents, because $1.40 equals 140 cents.