Here we have two mini investigations using addition skills and a little logic. The task is to put numbers into the circles so that each line adds up to 18. Each number can be used more than once so there are several different ways of doing this. The second page uses multiples of 10 to make 60. One of the easiest ways of doing this is to write the numbers on paper and cut them out, then move them about to see what the possibilities are. Triangular sums investigation