a) Find the biggest 6-digit integer number such that each digit, except for the two on the left, is equal to the sum of its two left neighbours.
b) Find the biggest integer number such that each digit, except for the first two, is equal to the sum of its two left neighbours. (Compared to part (a), we removed the “6-digit number” restriction.)
If \(R + RR = BOW\), what is the last digit of the number below? \[F \times A \times I \times N \times T \times I \times N \times G.\]
Shmerlin the magician found the door to the Cave of Wisdom. The door is guarded by Drago the Math Dragon, and also locked with a 4-digit lock. Drago agrees to put Shmerlin to the test: Shmerlin has to choose four integer numbers: \(x, y, z\) and \(w\), and the dragon will tell him the value of \(A \times x + B \times y + C \times z + D \times w\), where \(A, B, C\) and \(D\) are the four secret digits that open the lock. After that, Shmerlin should come up with a guess of the secret digits. If the guess is correct, Drago will let the magician into the cave. Otherwise, Shmerlin will perish. Does Shmerlin have a way to succeed?
A six-digit number starts with the digit \(1\). If this digit is relocated to the rightmost position, the number becomes \(3\) times bigger. What is the number?
Solve: \(HE \times HE = SHE\).
Shmerlin managed to enter the cave and explore it. On his way back, he was once again stopped by Drago. He learns that the door out of the cave is locked again, this time with a more powerful lock. The key required to open it now includes four positive integers, which are no longer digits – they can be much larger. Shmerlin once again can choose four integer numbers: \(x, y, z\) and \(w\), and the dragon will tell him the value of \(A \times x + B \times y + C \times z + D \times w\), where \(A, B, C\) and \(D\) are the four secret integer numbers that open the lock. Because the lock is much more difficult to crack now, Drago agrees to let Shmerlin try twice. He can choose his four integer numbers and then, basing on what he learns from the dragon, choose again. Will he be able to leave the cave or is he doomed to stay inside forever?
Integer numbers \(a,b\) and \(c\) are such that the sum of digits of a number \(a+b\) is less than \(5\), the sum of digits of a number \(b+c\) is less than \(5\), the sum of digits of a number \(a+c\) is less than \(5\), but the sum of digits of a number \(a+b+c\) is greater than \(50\). Can you find such three numbers \(a,b\) and \(c\)?
Lady X has 3 different black skirts, and 5 different jackets – 3 blue, and 2 green. She also has 10 different hats – 6 blue and 4 green. Lady X’s outfit consists of a skirt, a jacket, and a hat of the matching colour.
In how many ways can the Lady choose her outfit?
Let us call a number super-odd if it is made of odd digits only. (For example, numbers \(5\), \(33\), \(13573\) are all super-odd.) How many \(3\)-digit super-odd numbers with all digits different are there?
Among 7 girls in a group, exactly two of them are wearing red shirts. How many ways are there to seat all 7 girls in a row such that the two girls wearing red shirts are not sitting adjacent to each other?