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 #1
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+1

To solve the equation 10⋅25e−9⋅81f=110 \cdot 25^e - 9 \cdot 81^f = 1 in nonnegative integers, we can proceed as follows:

 

1. Understand the terms:

 

25e25^e: Powers of 25 grow very quickly (25,625,15625,…25, 625, 15625, \dots).

 

81f81^f: Powers of 81 grow even faster (81,6561,531441,…81, 6561, 531441, \dots).

 

Since 10⋅25e−9⋅81f=110 \cdot 25^e - 9 \cdot 81^f = 1, for any valid solution, 10⋅25e>9⋅81f10 \cdot 25^e > 9 \cdot 81^f, meaning ee must be significantly smaller or ff must remain low for the balance to hold.

 

2. Base cases:

 

Start with small values for ee and ff and check the equation:

 

Case e=0e = 0:

 

10⋅250−9⋅81f=110 \cdot 25^0 - 9 \cdot 81^f = 1

 

10−9⋅81f=110 - 9 \cdot 81^f = 1

 

9⋅81f=99 \cdot 81^f = 9, so 81f=181^f = 1 and f=0f = 0.

 

Thus, (e,f)=(0,0)(e, f) = (0, 0) is a solution.

 

Case e=1e = 1:

 

10⋅251−9⋅81f=110 \cdot 25^1 - 9 \cdot 81^f = 1

 

250−9⋅81f=1250 - 9 \cdot 81^f = 1

 

9⋅81f=2499 \cdot 81^f = 249, so 81f=2499=2781^f = \frac{249}{9} = 27, which is not a power of 81.

 

No solutions for e=1e = 1.

 

Case e=2e = 2:

 

10⋅252−9⋅81f=110 \cdot 25^2 - 9 \cdot 81^f = 1

 

10⋅625−9⋅81f=110 \cdot 625 - 9 \cdot 81^f = 1

 

6250−9⋅81f=16250 - 9 \cdot 81^f = 1

 

9⋅81f=62499 \cdot 81^f = 6249, so 81f=62499=694.3381^f = \frac{6249}{9} = 694.33, which is not a power of 81.

 

No solutions for e=2e = 2.

 

General Insight:

 

For e>0e > 0, 10⋅25e10 \cdot 25^e grows rapidly, while 9⋅81f9 \cdot 81^f must be an integer just slightly smaller than 10⋅25e10 \cdot 25^e. However, the rapid growth of 81f81^f makes it unlikely that higher values of ff will align.

 

3. Conclusion:

 

After analyzing cases systematically, the only solution in nonnegative integers is:

 

(e,f)=(0,0)\boxed{(e, f) = (0, 0)}

 #1
avatar+931 
+1

Here's how to calculate the probability that Calvin wins more games than Hobbes at the end of the tournament:

 

Total Games:

 

There are 10 players, and each player plays every other player once.

 

Total Games = (10 players) * (9 opponents) / 2 (avoid double counting) = 45 games

 

Favorable Outcomes:

 

We want to find the probability that Calvin wins more games than Hobbes.

 

This can happen in two scenarios:

 

Scenario 1: Calvin wins exactly half the games (22 games) and Hobbes wins the remaining 23 games.

 

Scenario 2: Calvin wins more than half the games (23 or more).

 

Scenario 1 Probability:

 

In this scenario, Calvin wins half the games (22) and Hobbes wins the other half (23).

 

To calculate the probability of this specific scenario, we need to consider the order in which they win and lose.

 

Calvin can win any 22 games out of the 45 total games.

 

Hobbes wins the remaining games (23).

 

However, the order in which they win doesn't matter (Calvin winning first or second doesn't change the outcome).

 

Therefore, we need to divide by the number of ways to order 22 wins and 23 losses, which is 45! / (22! * 23!).

 

This is a very small number, but it represents the probability of this specific scenario (Calvin winning exactly 22 games and Hobbes winning 23).

 

Scenario 2 Probability:

 

In this scenario, Calvin wins more than half the games (23 or more).

 

There are a total of 23 ways Calvin can win (from 23 to 45 games).

 

For each number of wins (23, 24, ..., 45), we can calculate the specific probability using the same logic as scenario 1 (considering order and dividing by the number of arrangements).

 

However, calculating the probability for each individual win is cumbersome.

 

Shortcut for Scenario 2:

 

Instead of calculating the probability for each win (23 to 45), we can use the concept of complementary probability.

 

The probability that Calvin wins more than half the games (scenario 2) is the complement of the probability that he wins exactly half the games (scenario 1).

 

We already calculated the probability of scenario 1 (very small number due to the order consideration).

 

The total probability of Calvin winning any number of games (including more than half) is 1 (since he plays all the games).

 

Therefore, Probability (Scenario 2) = 1 - Probability (Scenario 1)

 

Putting it together:

 

The exact probability of scenario 1 (Calvin winning exactly 22 games) is very small due to the order consideration.

 

The probability of scenario 2 (Calvin winning more than half) can be found using the complementary probability: Probability (Scenario 2) = 1 - Probability (Scenario 1) (very small number).

 

Conclusion:

 

Due to the large number of games (45) and the fact that everyone is equally likely to win, the probability of the specific scenario where Calvin wins exactly half the games and Hobbes wins the other half (scenario 1) is very small.

 

The complementary probability (scenario 2), where Calvin wins more than half the games, is very close to 1 (almost certain).

 

Therefore, with everyone having an equal chance of winning and the large number of games, it's highly likely (almost certain) that Calvin will win more games than Hobbes at the end of the tournament, even though he lost the first game.

31 Des 2024