If the remaining mass of u-237 in continuous fission is reduced in the same proportion as that of the previous day, the remaining mass is 50% of the original mass after 7 days of fission, and the remaining mass is 10% of the original mass after calculating the number of days of fission

If the remaining mass of u-237 in continuous fission is reduced in the same proportion as that of the previous day, the remaining mass is 50% of the original mass after 7 days of fission, and the remaining mass is 10% of the original mass after calculating the number of days of fission

Let the amount left every day be the original X
x^7=50%
x=(1/2)^(1/7)
Let it undergo y-day fission, leaving 10% of the original
x^y=10%
y=logx 0.1=log(1/2)^(1/7) 0.1=7log0.5 0.1=7lg0.1/lg0.5=-7/-0.301=23.3
That is, after about 23 days of fission, the remaining mass is 10% of the original mass