I'm with you on the last part, especially when the first part is itself a hard nut to crack.
At the beginning, we thought we would do only 45 challenges - because there are 45 cells. But we had more than 45 ideas so the extras were morphed into some of the challenges. For 7/1, this really isn't the case but for some of the challenges, you get two parts because of this reason.
In fact, at least two of the lower-level challenges which had two parts had one of the parts taken out and made into another challenge.