Which sample `A` or `B` shown in figure has shorter mean-life ?

Explanation

from the given figure we can say that
`"at " t= 0.((dN)/(dt))_(A) -((dN)/(dt))_(B)`
`rArr" "(N_(0))_(A) = (N_(0))_(B)`
Considering any instant t by drawing a line perpendicular to time axis we find that
`((dN)/(dt))_(A) gt ((dN)/(dt))_(B)` ,ltBrgt `rArr" " lambda_(A) N_(A) gt lambda_(B) N_(B)`
`:. " " N_(A) gt N_(B)" "("rate of decay of B is slower")`
`:. " "lambda_(B) gt lambda_(A)` ,
`:." "lambda_(B) gt lambda_(A)`
`rArr" "tau_(A) gt tau_(B)" "[:. "Average life" tau = 1/lambda]`