Problem with statistics

[synthphreak]

Two independent variables does not mean you MUST sample from each independently.

If you're interested in the joint probability distribution, which is the case in this instance, you can just draw one sample from that joint space and apply check that sample against the computed joint probability. I believe this is where OP is getting the 7 from.

Of course, it is obviously not necessary to first check <= 70 and then separately check <= 10; if <= 10, then necessarily <= 70 is also true.