### #1 - Hard Math Riddle

Take 9 from 6, 10 from 9, 50 from 40 and leave 6.

How Come ??

SIX - 9 (IX) = S
9 (IX) - 10 (X) = I
40 (XL) - 50 (L) = X
===>SIX

### #2 - Hardest Math Riddle

Create a number using only the digits 4,4,3,3,2,2,1 and 1. So i can only be eight digits. You have to make sure the ones are separated by one digit, the twos are separated by two digits the threes are separated with three digits and the fours are separated by four digits

41312432

### #3 - Mathematical Riddle

Using only two 2's and any combination of mathematical signs, symbols and functions can you make 5?

SQRT(.2 ^ -2)
Take .2 and raise it to the power of -2 and then take the square root.

### #4 - February Series Question

Find The Next Number
12 13 15 17 111 113 117 119 123 ?

129.

These are the first 10 prime numbers (2, 3, 5...) prefixed with a 1

### #5 - Hard Maths Riddle

Using the digits 1 up to 9, two numbers must be made. The product of these two numbers should be as large as possible. All digits must be used exactly once. Which are the requested two numbers. ?

The digits of the requested two numbers obviously form descending sequences. Furthermore, if you have two pairs of numbers with equal sums, the pair of which the numbers have the smallest absolute difference, is the one of which the numbers have the largest product. Using this knowledge, the two numbers can easily be constructed by placing the digits one by one, starting with 9 and ending with 1:
9

8 -> 96

87 -> 964

875 -> 9642

8753 -> 9642

87531
Conclusion: the requested two numbers are 9642 and 87531 (and the product of these two numbers is 843973902).