How do I interpret bank interest? I always have trouble understanding it. Take Singlife and UOB One Account as an example, can anyone advise?

Singlife: Balance 20k
2.5% p.a First S$10,000, 1% p.a Next S$90,000

Does it mean: (a)
1) $500 - $10,000 => 2.5% p.a
2) $10,001 - $20,000 => 1% p.a
Final interest = interest received from 1 + 2

or (b)
The full $20.000 => 1% p.a

UOB One Account: Balance 80k
1,25% First $15,000, 1.30% Next $15,000, 1.35% Next $15,000, 1.40% Next $15,000, 3.68% Next $15,000, Above, $75,000 $0.05%

How do I calculate the interest for both Singlife and UOB One Account with the balance indicated.