Rich picked 3 1/2 pints of strawberries and used 4/5 of them to make jam. How many pints of strawberries did he use for the jam?

To calculate the pints of strawberries Rich used for jam, we need to multiply the amount of strawberries he picked by the fraction used to make jam: 3 1/2 pints * 4/5 = <<3 1/2*4/5=2.8>>2.8 pints. Answer: \boxed{2.8}.