Which number should replace the question mark?
3 1 4 7 2 9 1 5 ?
3 and 1 add to 4 7 and 2 add to 9 1 and 5 must be adding to 6
3+1=4, 7+2=9, 1+5=6
Which number should replace the question mark in the picture below ?
5 12 15 7 9 4 23 87 ?