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24 votes
6 answers
9k views

What is the sum of all positive even divisors of 1000?

11 votes
6 answers
843 views

To find whether $a$ is a prime number

11 votes
7 answers
3k views

What is the sum of the $81$ products in the $9 \times 9$ multiplication grid?

8 votes
1 answer
399 views

What is the probability that they have no common prime factor?

8 votes
6 answers
508 views

Find the value of $\frac{a^2}{a^4+a^2+1}$ if $\frac{a}{a^2+a+1}=\frac{1}{6}$

6 votes
1 answer
18k views

What is the smallest composite number

6 votes
3 answers
1k views

find the largest number

5 votes
3 answers
549 views

Find the last digit of $3^{1999}$

5 votes
2 answers
939 views

At least how many students like all the activities?

4 votes
2 answers
464 views

Prove the number of divisors

3 votes
2 answers
55 views

Find the smallest real value of $x$

3 votes
1 answer
47 views

Find the other factor

3 votes
2 answers
1k views

If $x$ and $y$ are positive numbers less than $20$ for which $x+y+xy=76$, what is $x+y$?

3 votes
3 answers
641 views

What is the sum of the prime factors of $2^{16}-1$?

3 votes
2 answers
401 views

How many ways can all six numbers in the set $\{4, 3, 2, 12, 1, 6\}$ be ordered

3 votes
1 answer
2k views

How many positive two-digit integers have exactly 8 positive factors?

3 votes
2 answers
1k views

how many distinct values does it have?

3 votes
3 answers
115 views

A question about $ax = b$

2 votes
2 answers
38 views

given an equation, find A and B

2 votes
2 answers
831 views

How many three-digit primes less than 200 have two digits the same?

2 votes
4 answers
751 views

What is the smallest possible value of $n$?

2 votes
2 answers
299 views

What is the largest prime factor of $55^{100}+55^{101}+55^{102}$

2 votes
4 answers
1k views

For how many positive integers $a$ is $a^4−3a^2+9$ a prime number?

2 votes
2 answers
547 views

The sum of the cubes of two different prime numbers is 5256.

2 votes
4 answers
224 views

What is the value of $x$ in $222^x−111^x∗7=111^x$?

2 votes
2 answers
137 views

Use the $\epsilon-\delta$ definition of limit to prove that $\lim\limits_{x\to2}x^2 = 4$

2 votes
2 answers
362 views

how many of the resulting number are divisible by 11 but not by 5?

1 vote
6 answers
560 views

Find the real solutions of the equations:$x+y=2$, $xy-z^2=1$

1 vote
1 answer
76 views

Seven-element lists of integers with conditions on means

1 vote
1 answer
595 views

What is the volume of this octahedron?