Find the 2-digit number CA, given that A and C are two non-zero digits and the 2-digit numbers formed by these two digits have the following properties: 1. CA is divisible by 13; 2. AC is a square number;
5 numbers, A, B, C, D and E, represent different numbers from 1 to 9. Given the following conditions: 1. The sum of A and E is less than the sum of C and 5. 2. The sum of A, C and E equals D. 3. The sum of A and D equals B. 4. D is divisible by C. 5. The sum of A and C is less than E. 6. D is greater than 6. Find the number to represent D.
A stationery store had a batch of ball pens. One half but 6 fewer pens were sold on the first day. One half of the remaining part and 8 more pens were sold on the second day. Finally, 20 ball pens are left. How many ball pen(s) did the stationery store have originally?
John wrote a four-digit number with all digits different. Guess 1703 has two correct digits in correct positions; guess 2745 has two correct digits in wrong positions; guess 3541 has all digits correct but all in wrong positions. Find the number.
Given that there are 12 signs of the zodiac, at least how many student(s) is / are there such that there exists at least 11 of them having the same sign of the zodiac?