What is a remainder of \(7780 \times 7781 \times 7782 \times 7783\) when divided by \(7\)?
Tim had more hazelnuts than Tom. If Tim gave Tom as many hazelnuts as Tom already had, then Tim and Tom would have the same number of hazelnuts. Instead, Tim gave Tom only a few hazelnuts (at most five) and divided his remaining hazelnuts equally between \(3\) squirrels. How many hazelnuts did Tim give to Tom?
Prove that \(n^3 - n\) is divisible by \(24\) for any odd \(n\).
Show that if numbers \(a-b\) and \(c-d\) are divisible by \(11\), then \(ac-bd\) and \(ad - bc\) are also both divisible by \(11\).
For how many pairs of numbers \(x\) and \(y\) between \(1\) and \(100\) is the expression \(x^2 + y^2\) divisible by \(7\)?
Seven robbers are dividing a bag of coins of various denominations. It turned out that the sum could not be divided equally between them, but if any coin is set aside, the rest could be divided so that every robber would get an equal part. Prove that the bag cannot contain \(100\) coins.
Show that the equation \(x^2 +6x-1 = y^2\) has no solutions in integer \(x\) and \(y\).
Catherine asked Jennifer to multiply a certain number by 4 and then add 15 to the result. However, Jennifer multiplied the number by 15 and then added 4 to the result, but the answer was still correct. What was the original number?
The product of two natural numbers, each of which is not divisible by 10, is equal to 1000. Find the sum of these two numbers.
Does there exist a natural number which, when divided by the sum of its digits, gives a quotient and remainder both equal to the number 2011?