I have tried defining A=10 and B=20 C=30 D=40

When i put SUM(A+B) the figure is correct which is 30

But how do i just click SUM and use my mouse to drag the cells with A B C D and the sum is shown 100.

I trid and it shows 0. I knw i have to name or label it for even if A is shown it is 10 value. But if we just enter A and B and when you sum it, you cant unless i key into the formula area SUM(A+B)

HELP!