4.5 b乓_)7 Answer Explanationsby the formula勹）p飞1—p)"-x.For the problem
at hand, it is given that each child is equally
likely to be a boy or a girl, and so p =—^1 .Thus,
2
the probability of having exactly 2 girls born to a
couple with 4 children is丿IW
H
]'厂
，且
）'(½
)'=
Th e correct answer 1 s A.
PS01564- The closing price of Stock X changed on each trading
day last month. (^) The percent change in the closing
price of Stock X from the first trading day last month
to each of the other trading days last month was less
than 50 percent. If the closing price on the second
trading day last month was $10.00, which of the
following CANNOT be the closing price on the last
trading day last month?
(A) $3.00
(B) $9.00
(C) $ (^19). 00
(D) $ 24. 00
(E) $ (^29). 00
Arithmetic
Let P be the first-day closing price, in dollars, of
the stock. It is given that the second-day closing
price was (1 + n%)P = 10, so P =^10 , for
l+n%
some value of n such that-SO< n < 50. Therefore,
Pis between^10 ""6.67 and^10 =20.
1 + 0.50 1 -0.50
Hence, if Q is the closing price, in dollars, of
the stock on the last day, then Q is between
(0.50)(6.67) "" 3.34 (50% decrease from the
lowest possible first-day closing price) and
(1.50)(20) = 30 (50% increase from the greatest
possible first-day closing price). The only answer
choice that gives a number of dollars not between
3.34 and 30 is the first answer choice.
Th e correct answer 1s A.
PS02389
- In the figure above, point O is the center of the circle
and OC =AC= AB. What is the value of x?
(A) 40
(B) 36
(C) 34
(D) 32
(E) 30Geometry 1qk,sDBBConsider the figure above, where DB is a
diameter of the circle with center O and AD is a
chord. Since OC=AC, l:::.OCA is isosceles and so
the base angles, LAOC and乙OAC, have the same
degree measure. The measure of乙1.0C is given as
x^0 , so the measure of乙OACis x^0. SinceAC=AB,
!::.CAB is isosceles and so the base angles, 互CB
and乙1.BC,have the same degree measure. The
measure ——of each is marked as y O. Likewise, since
OD and OA are radii of the circle, OD = OA, and
!::.DOA is isosceles with base angles, LADO and
乙DAO, each measuring z^0. Each of the following
statements is true: