Our balance sheet continues to get stronger, with cash and cash equivalents, other investments and marketable securities increasing 31% to $87.5 million as compared to $66.7 million at June 30, 2023, We have no debt and the net cash provided by operating activities for the nine months ended March 31, 2024 was also strong, amounting to $31.0 million.
Our Alarm Lock and Marks locking hardware lines continue to see growth in school and classroom security, healthcare, and retail loss-prevention, as well as in multi-dwelling commercial and residential applications. Locking sales in Q3 grew approximately 16% compared to last year and approximately 10% compared to Q2 and represents 66% of hardware sales. We continue to remain focused on further penetrating each of these markets.
We recently announced the introduction of Prima by NAPCO, a new All-in-One Panel for security, fire, video and connected home. Our goal is for Prima to address an important mass segment of the security market, including residential and small business systems. With built-in Wi-Fi/cellular radio communications, customer alert notifications, and video and smart home subscription options for each -installed system, the security dealer, as well as the Company, can add more recurring-revenue generating accounts.
NAPCO's record-breaking results for Q3 of fiscal year 2024, was primarily the result of the continued growth and profitability from recurring revenues as well as the strong sales from our Alarm Lock and Marks locking product lines. Radio sales in Q3 improved over Q2, increasing by approximately 2%. We expect radio sales to continue to be a key contributor to our hardware sales and continue to lead to the continued growth of our highly profitable recurring revenues."
Mr. Soloway concluded, "We are nine months through fiscal 2024 and while we have already generated net income of $36.3 million, Adjusted EBITDA* of $43.5 million and our Adjusted EBITDA* margin is now 31%, there is more work to be done. While we continue to be encouraged with the gross margin for hardware sales of 29%, we believe this could improve further in Q4 and beyond. Our strong net income and Adjusted EBITDA* margins indicate the financial strength of our business. As such, we are pleased to continue our dividend program and we will be paying another dividend of $0.10 per share on June 24, 2024. As always, we will strive to accomplish our goal of continued financial strength, product innovation, technical superiority, and strong profitability, for the balance of fiscal 2024 and beyond".
Financial Results
Net sales for the quarter increased 13% to $49.3 million (the highest quarterly sales in the Company's history), as compared to $43.5 million for the same period one year ago. Net sales for the nine months ended March 31, 2024 increased 10% to a nine month record $138.5 million, as compared to $125.3 million for the same period one year ago. Research and development costs for the quarter increased 19% to $2.8 million, or 6% of sales, as compared to $2.3 million or 5% of sales for the same period a year ago. Research and development costs for the nine months ended March 31, 2024 increased 11% to $7.7 million, or 6% of sales, as compared to $7.0 million or 6% of sales for the same period a year ago. Selling, general and administrative expenses for the quarter increased 10% to $9.2 million or 19% of net sales, as compared to $8.4 million, or 19% of sales for the same period last year. Selling, general and administrative expenses for the nine months ended March 31, 2024 increased 6% to $26.3 million or 19% of net sales, as compared to $24.7 million, or 20% of sales for the same period last year.
Operating income for the quarter increased 38% to $14.5 million as compared to $10.5 million for the same period last year. Operating income for the nine months ended March 31, 2024 increased 115% to $39.9 million as compared to $18.5 million for the same period last year. Net income for the quarter increased 38% to a quarterly record $13.2 million, or $0.36 per diluted share, as compared to $9.5 million, or $0.26 per diluted share, for the same period last year and represents 27% of net sales. Net income for the nine months ended March 31, 2024 increased 119% to a nine month record of $36.3 million or $0.98 per diluted share as compared to $16.6 million or $0.45 per diluted share for the same period last year and represents 26% of net sales.
Adjusted EBITDA* for the quarter increased 37% to a quarterly record $15.6 million, or $0.42 per diluted share, as compared to $11.3 million, or $0.31 per diluted share for the same period last year and equates to an Adjusted EBITDA* margin of 32%. Adjusted EBITDA* for the nine months ended March 31, 2024 increased 105% to a nine month record $43.5 million, or $1.18 per diluted share, as compared to $21.3 million, or $0.57 per diluted share for the same period last year and equates to an Adjusted EBITDA* margin of 31%.
Balance Sheet Summary
As of March 31, 2024, the Company had $87.5 million in cash and cash equivalents, other investments and marketable securities as compared to $66.7 million as of June 30, 2023. Working capital (defined as current assets less current liabilities) was $138.3 million at March 31, 2024 as compared with working capital of $111.7 million at June 30, 2023. Current ratio (defined as current assets divided by current liabilities) was 7.9:1 at March 31, 2024, and 6.7:1 at June 30, 2023.
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