DDB depreciation in each year is 2/5 of the carrying value at the beginning of the year, until the carrying value reaches the estimated salvage value.
Year 1 DDB depreciation = $20,000 × 2/5 = $8,000
Carrying value = $20,000 – $8,000 = $12,000
Year 2 DDB depreciation = $12,000 × 2/5 = $4,800
Carrying value = $12,000 – $4,800 = $7,200
Year 3 DDB depreciation = $7,200 × 2/5 = $2,880
Because $7,200 – $2,880 = $4,320 would depreciate the equipment below its salvage value, depreciation in Year 3 is limited to $7,200 – $5,000 = $2,200.