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the right is the ratio of that part of the figure A / B 
de fcri bed as before which is intercepted between 
perpendiculars erected upon A B at the points f 
and b, to the whole figure A i B. 
For, there being thefe two fubfequent events, 
the firfi that the point o will lie between f and b ; 
the fecond that the event M fhould happen p times 
and fail q in p q trials ; and (by cor. prop. 8.) the 
original probability of the fecond is the ratio of 
A i B to C A, and (by prop. 8.) the probability of 
both is the ratio of j'g h im b to C A; wherefore 
(by prop. it being firfi difeovered that the fecond 
has happened, and from hence I guefs that the 
firff has happened alfo, the probability I am in 
the right is the ratio of fghimb to A/B, the 
point which was to be proved. 
Cor. The fame things fuppofed, if I guefs that 
the probability of the event M lies fomewhere be- 
tween o and the ratio of A b to A B, my chance 
to be in the right is the ratio of A b m to A / B. 
Scholium. 
From the preceding propofition it is plain, that 
in the cafe of fuch an event as I there call M, from 
the number of times it happens and fails in a cer- 
tain number of trials, without knowing any thing 
more concerning it, one may give a guefs where- 
abouts it’s probability is, and, by the ufual methods 
computing the magnitudes of the areas there menti- 
oned, fee the chance that the guefs is right. And that 
the fame rule is the proper one to be ufed in the cafe 
of an event concerning the probability of which 
we 
