[填空题]
A typical banana contai6 wrx h90ttxs,a ltmayf gzeq:9jq43. 5cc44xns 400 mg of potassium, of which a smal6 entp7kt,xn9jf q n61l fraction is the radioactive isotopn6 en9qtfj,k 7 tp6n1xe $_{19}^{40}\text{K}$ (see Appendix B). Estimate the activity of an average banana due to $_{19}^{40}\text{K}$. $\lambda N$ = $\ \text{decays/s}$
