40 slices per watermelon and each slice having 20 black seeds means each watermelon has 20*40=<<20*40=800>>800 black seeds.
40 slices per watermelon and each slice having 20 white seeds means each watermelon has 20*40=<<20*40=800>>800 white seeds.
In total, each watermelon has 800+800=<<800+800=1600>>1600 seeds.
What is the total number of seeds in a watermelon?
#### 1,600