1. Which number replaces the question mark?
Answer: 10
Explanation: Working in columns, the sum of the numbers in each column equals 23.
2. Which number replaces the question mark?
Answer: 7
Explanation: In each square, multiply the top and bottom numbers together to give a 2 digit result, and put the letters with the numerical values of each digit in the left and right hand spaces.
3. Which number replaces the question mark?
Answer: 13
Explanation: Working in rows, from left to right, double the left hand number to get the middle number, and add 3 to this to get the right hand number.
4. Which number replaces the question mark?
Answer: 38
Explanation: Starting at the top, add 4 to the first number to get the second, then add 5, 6, 7 etc.
5. Which number replaces the question mark?
Answer: 3
Explanation: Using the lower two circles as a source, the values in corresponding segments of the upper left circle equal the sums of the numbers in the lower two circles. The values in the upper central circle equal the products of the values in the lower two circles, and the upper right circle equals the difference between values in the lower two circles.