Find the amount of each ingredient remaining, then the percentage of total.<br><br>\\(\begin{aligned}<br>\text{Flour used} &= 15 \times 0.40 = 6 \text{ kg}, & \text{remaining} &= 9 \text{ kg}<br>\\<br>\text{Sugar used} &= 8 \times 0.25 = 2 \text{ kg}, & \text{remaining} &= 6 \text{ kg}<br>\\<br>\text{Total ingredients} &= 15 + 8 = 23 \text{ kg}<br>\\<br>\text{Total remaining} &= 9 + 6 = 15 \text{ kg}<br>\\<br>\text{Percentage not used} &= \frac{15}{23} \times 100\% = 65\frac{5}{23}\%<br>\end{aligned}\\)<br><br>Final Answer: \\(65\frac{5}{23}\%\\) (approximately 65.22%)