What percent of 21 is 7?

a) 21 = p * 7; 300%
b) 21 = p * 7; 33.33%
c) 7 = p * 21; 300%
d) 7 = p * 21; 33.33%

you & happy new years!

step-by-step explanation:

the original amount doesn't ''re just looking for the time it takes for 1/2 of the substance to we have

(1/2) =)     take the ln   of both sides

ln (1/2)   = )   and we can write

ln(1/2) = ) lne     and lne   = 1     so we have

ln(1/2) = -.1092t     divide both sides by -.1092

t = ln(1/2)/-.1092 = about 6.347 days = about 6.3 days (rounded)