OlympiadHardCombinatorics5–6

In how many ways can $20$ cents be paid using only $5$ -cent and $10$ -cent coins? Two ways are the same if they use the same number of each coin.

De quantas maneiras se podem pagar $20$ cêntimos usando apenas moedas de $5$ e de $10$ cêntimos? Duas maneiras são iguais se usarem o mesmo número de cada moeda.

Answer options

Solution

Step 1 of 3

1.Count by the number of $10$ -cent coins.

In how many ways can 202020 cents be paid using only 555-cent and 101010-cent coins? Two ways are the same if they use the same number of each coin.

Answer options

In how many ways can $20$ cents be paid using only $5$ -cent and $10$ -cent coins? Two ways are the same if they use the same number of each coin.