Prove that if \(p\) is a prime number and \(1 \leq k \leq p - 1\), then \(\binom{p}{k}\) is divisible by \(p\).
Prove that if \(p\) is a prime number, then \((a + b)^p - a^p - b^p\) is divisible by \(p\) for any integers \(a\) and \(b\).
The numbers \(1, 2,\dots ,99\) are written on 99 cards. Then the cards are shuffled and placed with the number facing down. On the blank side of the cards, the numbers \(1, 2, \dots , 99\) are once again written.
The sum of the two numbers on each card are calculated, and the product of these 99 summations is worked out. Prove that the end result will be an even number.
Prove that any \(n\) numbers \(x_1,\dots , x_n\) that are not pairwise congruent modulo \(n\), represent a complete system of residues, modulo \(n\).
Write the following rational numbers in the form of decimal fractions: a) \(\frac {1}{7}\); b) \(\frac {2}{7}\); c) \(\frac{1}{14}\); d) \(\frac {1}{17}\).
Let the number \(\alpha\) be given by the decimal:
a) \(0.101001000100001000001 \dots\);
b) \(0.123456789101112131415 \dots\).
Will this number be rational?
Prove that the number \(\sqrt {2} + \sqrt {3} + \sqrt {5} + \sqrt {7} + \sqrt {11} + \sqrt {13} + \sqrt {17}\) is irrational.
There are 4 weights and scales. How many loads that are different by weight can be accurately weighed using these weights, if
a) weights can be placed only on one side of the scales;
b) weights can be placed on both sides of the scales?
a) One person had a basement illuminated by three electric bulbs. Switches of these bulbs are located outside the basement, so that having switched on any of the switches, the owner has to go down to the basement to see which lamp switches on. One day he came up with a way to determine for each switch which bulb it switched on, descending into the basement exactly once. What is the method?
b) If he goes down to the basement exactly twice, how many bulbs can he identify the switches for?
Will thought of a number: 1, 2 or 3. You can ask him only one question, to which he can answer “yes”, “no” or “I do not know”. Can you guess the number by asking just one question?