Stem, wash, and crush strawberries. (A potato masher works nicely.) Measure 3 1/4 cups into a large pot.
Mash bananas, and measure 1 1/2 cups into the pot.
Stir in lemon juice, and then pectin. Bring to a full rolling boil on high heat, stirring constantly. Dump in sugar. Return to full boil and boil 1 minute, stirring constantly.
Remove from heat.
Spoon into hot, clean jars. Screw lids on. Process in a water bath for 10 minutes.