Why is it that i write with my right hand but do mostly everything else with my left?

I'm right handed, been all my life, but i only write with my right hand. I wash the dishes with my left, when i snowboard im goofy (right in front instead of left), and when i put my hands together, my left thumb is on top, but my sister (who is also right handed) does this, her right thumb is on top? I kinda just wanna know why im like this, im not freaking out or anything, I just find it reallly odd.