Table:
|  |  | Year Ended March 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
| Net sales | 100.0% | 100.0% | 100.0% |
| Cost of sales | 45.2 | 39.2 | 48.4 |
| Gross profit | 54.8 | 60.8 | 51.6 |
| Research and development | 15.4 | 13.3 | 16.0 |
| Selling, general and administrative | 12.8 | 11.4 | 14.7 |
| Amortization of acquired intangible assets | 12.6 | 12.2 | 9.9 |
| Special charges and other, net | 0.6 | 0.4 | 2.9 |
| Operating income | 13.4% | 23.5% | 8.1% |
Paragraphs:
Results of Continuing Operations
The following table sets forth certain operational data as a percentage of net sales for the fiscal years indicated:
Question:
What was the percentage change in operating income of net sales between 2018 and 2019?
Answer: 13.4-23.5 = -10.1