Thomas has been saving for six years, and since each year has 12 months, he has been making savings for 6*12 = <<6*12=72>>72 months.
Since Thomas has been saving $40 in the bank every month for six years, he has saved 72*$40 = $<<72*40=2880>>2880
Joseph has been saving 2/5 times less money per month than Thomas, meaning he has been saving 2/5*$40 = $<<2/5*40=16>>16 less per month.
The total amount of money that Joseph has been saving per month is $40-$16 = $<<40-16=24>>24
In six years, Joseph has saved $24*72 = $<<24*72=1728>>1728
Together, they have saved a total of $2880+$1728 = $<<2880+1728=4608>>4608
#### 4608