If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Lesson 9: Money

Counting dollars

Sal adds to find the total value when given an amount US dollars.

Want to join the conversation?

• You have in front of you 435 ​five-dollar bills and 855 ​ten-dollar bills. Your​ problem: Place the​ five-dollar bills and the​ ten-dollar bills in stacks so that each stack has the same number of​ bills, and each stack contains only one kind of bill​ (five-dollar or​ ten-dollar). What is the largest number of bills that you can place in each​ stack?
• The number of bills in each stack must be a common factor of the number of \$5 bills, 435, and the number of \$10 bills, 855. So the largest number of bills in each stack is the greatest common factor of 435 and 855. (Note that the actual values of the bills, \$5 and \$10, do not matter in this problem. What matters is that the bills are of two different kinds.)

The prime factorization of 435 is 3*5*29.
The prime factorization of 855 is 3*3*5*19.

When we construct the greatest common factor (GCF), we use each possible prime factor the smallest number of times it occurs in any prime factorization.

The prime factor 3 is used once and twice in the prime factorizations, so we use it once in the GCF.
The prime factor 5 is used once and once in the prime factorizations, so we use it once in the GCF.
The prime factor 19 is used zero times and once in the prime factorizations, so we use it zero times in the GCF.
The prime factor 29 is used once and zero times in the prime factorizations, so we use it zero times in the GCF.

So the GCF is 3*5, which is 15. Therefore, the greatest number of bills in each stack is 15.

Have a blessed, wonderful day!
• How much is the eagle coin
• The American Golden Eagle coin is worth \$1.00
• How much in Indian rupees is 1 dollar
• IS there a unit that will help with returning money? For example: A cashier reads a total, the customer gives them an amount; how much should the cashier return?
• You can use subtraction (with 2 decimal places) to help figure out how much change to give a customer.

For instance, let's say the cashier is handed a \$20 dollar bill for a stuffed animal that costs \$13.99

\$20.00
-13.99
_____
\$6.01