+293 Radium-221 has a half-life of 30 sec. How long will it take for 76% of a sample to decay? (Round your answer to the nearest whole number.)
+36916 amountleft = amount (1-.5)n Where n = number of half lifes amount left = 1 - .76 = .24
.24 = (1-.5)n
.24 = .5n Log both sides
log .24 = n log .5
log .24 / log .5 = n
n = 2.0589 half lifes = 61.77 seconds
