1. **State the problem:** We have an element with an initial mass of 250 grams that decays by 17.3% per minute. We want to find how much of the element remains after 18 minutes, rounded to the nearest tenth of a gram. 2. **Formula used:** The exponential decay formula is: $$m(t) = m_0 \times (1 - r)^t$$ where: - $m(t)$ is the mass remaining after time $t$, - $m_0$ is the initial mass, - $r$ is the decay rate per unit time (as a decimal), - $t$ is the time elapsed. 3. **Identify values:** - $m_0 = 250$ grams - $r = 0.173$ (17.3% decay per minute) - $t = 18$ minutes 4. **Calculate remaining mass:** $$m(18) = 250 \times (1 - 0.173)^{18} = 250 \times (0.827)^{18}$$ 5. **Evaluate the power:** Calculate $(0.827)^{18}$: $$0.827^{18} \approx 0.0423$$ 6. **Multiply to find remaining mass:** $$m(18) = 250 \times 0.0423 = 10.575$$ 7. **Round to nearest tenth:** $$10.575 \approx 10.6$$ grams **Final answer:** After 18 minutes, approximately **10.6 grams** of the element remain.