A · Fundamentals · §6
What a keepable seven looks like, with the actual numbers.
The hands this deck keeps are defined by whether they do something on turn one and whether they can cast two spells on turn two.
The relevant figures on the exact sixty, before any mulligan: two or more lands in 68.6% of sevens, at least one one-mana threat in 65.4%, and both together in 41.6%. A Cutter appears in 39.9%.