Cost

Product Development in Progress $($ millions$)$

Capitalized Product Development $($ millions$)$

Balance at $31$ March $2016$

$1,539$

$4,525$

Additions$$internally developed

$1,426$

$$

Transfers

$(809)$

$809$

Disposals

$$

$(138)$

Balance at $31$ March $2017$

$2,156$

$5,196$

Amortization

Balance at $31$ March $2016$

$$

$1,635$

Amortization for the year

$$

$769$

Disposals

$$

$(138)$

Balance at $31$ March $2017$

$$

$2,266$

Net book value at $31$ March $2017$

$2,156$

$2,930$

Estimate the average useful life of product development costs by dividing average capitalized product development costs by the amortization expense for fiscal $20162017.$ Compute average capitalized product development costs as simple average balances at the beginning and end of each fiscal year. Does your estimate fall within the range of the useful lives for development costs disclosed in the accounting policy footnote?