A fixed read-base numerator shows how genome size changes acceptance. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The read-base numerator stays fixed
The source still has 24 unique reads at read length 50, so the numerator is 1200 read bases.
24⋅50=1200
A smaller genome denominator raises coverage
Genome size 300 gives coverage 4x and accepted bit 1.
1200/300=4≥3
The middle genome size is the boundary
Genome size 400 gives exactly 3x coverage, so equality accepts.
1200/400=3≥3
The large denominator fails the same gate
Genome size 600 gives coverage 2x, so the accepted bit is 0.