3. What is the yearly rent of 50L. to continue 5 years, worth in ready money, at 5 per cent.?

Ans. 216L. 9s. 10d. 2.24qrs.

ANNUITIES TAKEN IN REVERSION,

AT COMPOUND INTEREST.

Annuities taken in reversion, are certain sums of money payable yearly for a limited period, but not to commence till after the expiration of a certain time.

CASE 1.

The annuity, time of reversion, time of continuance, and rate given, to find the present worth of the annui ty in reversion:

RULE."

Divide the annuity by the ratio involved to the time of continuance, and subtract the quotient from the annuity for a dividend; multiply the ratio involved to the time of reversion by the ratic, less one, for a divisor; the quotient of this division will be the present worth. Or,

Take two numbers under the given rate in Table IV. viz. that opposite the sum of the two given times, and that against the time of reversion, and multiply their difference by the annuity of the present worth.

When the payments are half yearly or quarterly, use Table V.

EXAMPLES.

1. What is the present worth of a reversion of a lease of 40L. per annum, to continue for six years, but not to commence till the end of 2 years, allowing 6 per cent. to the purchaser?

Ratio in-7

}

40 annuity.

volved to=1.4185191)40.000000000000(28.19842 the time.

11.80158

1.06×1.06.06.067416)11.50158(175.056+L. Ans. Or by Table IV. First, the sum of the two given

times is 8 years, and the time of reversion 2 years, therefore,

Take for 8 years 6.20979

for 2 do. 1.83339

Difference 4.37640

X40 annuity.

L. 175.05600 Ans. as before.

2. A person owns a farm which he proposes to let for 8 years, at 100 dollars per annum; but cannot give possession till after the expiration of two years; what is the present worth of such a lease, allowing 4 per cent. for present payment? Ans. 622.48 dols. 3. What is the present worth of a reversion of a lease of 60 L. per annum, to continue 7 years, but not to comence till the end of 3 years, allowing 5 per cent. to the purchaser ? Ans. 299 L. 18 s. 2.112 d.

PERPETUITIES,

AT COMPOUND INTEREST.

Perpetuities are such annuities as continue for ever.

CASE 1.

The annuity, and rate given, to find the present worth.

RULE.

Divide the annuity by the ratio less one, for the pre sent worth.

Note. For perpetual half yearly, or quarterly payments, Table V. is to be applied as in similar cases of temporary annuities.

EXAMPLES.

1. What is an estate of 140 L. per annum, to continue for ever, worth in present money, allowing 4 per cent. to the purchaser ?

L.

1.04—1=.04)140.00

L. 3500

2. What is the present worth of a freehold estate of 290 dollars per annum, to continue for ever, allowing 4 per cent. to the purchaser ?

Ans. 7250 dols.

PERPETUITIES IN REVERSION.

CASE 1.

The rent of a freehold estate, time of reversion, and rate per cent. given, to find the present worth.

RULE.

Multiply the ratio involved to the time of reversion, by the ratio, less one, for a divisor; by which divide the yearly payment, the quotient will be the answer.

EXAMPLES.

1. If a freehold estate of 50 L. per annum, to commence 4 years hence, be put up at sale, what is the present worth, allowing the purchaser 5 per cent.?

Ans. 822 L. 14 s. 1 d. 2 qrs. +

Ratio involved to the time of reversion, viz. 4 years S

1.2155062

.05 ratio less one.

.060775310)50(822 7. 14s. 1 d. 2q.+ 2. What is an estate of 696 dols. per annum, to continue for ever, but not to commence till the expiration of 4 years, worth in present money, allowance being made at 4 per cent.?

Ans. 14873.594 dols.

PERMUTATION.

Permutation is a rule for finding how many different ways any given number of things may be varied in position, place, or succession; thus, a b c, a c b, b a c, b ca, ca b, c b a, are six different positions of three

letters.

RULE.

Multiply all the terms of the natural series continually from one to the given number inclusive; the last product will be the answer required.

R

EXAMPLES.

1. In how many different positions can 6 persons place themselves at a table? 1x2x3x4x5×6=720. Ans. 2. How many days can 7 persons be placed in a different position at dinner? Ans. 5040 days. 3. What number of changes may be rung upon 12 bells, and in what time may they be rung, allowing 3 seconds to every change.

Ans.

479001600 changes. (45 years, 195 days, 18 hours.

COMBINATION.

Combination is a rule for discovering how many different ways a less number of things may be combined out of a greater; thus out of the letters a, b c, are three different combinations of two; viz. ab, ac, b..

RULE.

Take a series proceeding from and increasing by a unit, up to the number to be combined; and another series of as many places decreasing by a unit, from the number out of which the combinations are to be made, multiply the former continually for a divisor, and the latte for a dividend, the quotient will be the answer.

EXAMPLES.

1. How many combinations can be made of 5 letters out of ten?

10×9×8×7×6

-=252. Ans.

1×2×3×4X5

2. How many combinations can be made of 6 letters out of 10?

Ans. 210 3. What is the value of as many different dozens as may be chosen out of 24, at 1 d. per dozen.

Ans. 11267 L. 6 s. 4 d.

DUODECIMALS.

Duodecimals are fractions of a foot, or of an inch, or parts of an inch, &c. having 12 for their denominator.

The denominations are, foot, inch, second, third, and fourth.

4. Four floors in a certain building contain each 1084 feet, 9 in. 8"; how many feet are there in all? Ans. 4339 ft. 2 in. 8". 5. There are six mahogany boards, the first measures 27ft. 3 in., the second, 25 ft. 11 in., the third, 23 ft. 10 in., the fourth, 20 ft. 9 in., the fifth, 20 ft. 6 in., and the sixth, 18ft. 5 in.; how many feet do they contain?

Ans. 136 ft. 8 in.

4. If 19 ft. 10 in. be cut from a board which contains

41 ft. 7 in., how much will be left?

Ans. 21 ft. 9 in.