# Task No. 7.1

## Condition:

On the Misty Planet, santiks, kubriks, and tugriks are in circulation. One santik can be exchanged for 1 kubrik or 1 tugrik, 1 kubrik can be exchanged for 3 santiks, and 1 tugrik can be exchanged for 4 santiks. No other exchanges are allowed. Jolly U, initially having 1 santik, made 20 exchanges, and now he has 25 santiks (and no other money). How many times did he exchange kubriks for santiks?
# Answer: 6

## Exact match of the answer -1 point

## Solution.

To increase the number of santiks, we need to exchange them for kubriks or tugriks. In essence, we need to perform a double exchange, that is, first convert a santik into a tugrik or kubrik at a 1:1 ratio, and then increase the number of coins. Since the total number of exchanges is 20, 10 "double exchanges" were conducted. When exchanging a kubrik, the number of coins increases by 2, and when exchanging a tugrik, it increases by 3. Starting with 1 coin, it became 25 - the number of coins increased by 24. If all exchanges were made using kubriks, the number of coins would have increased by 20. In our case, it increased by 24, so 4 exchanges were made with tugriks, and 6 with kubriks.

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