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Prof. M A ThiruthuvadossCell: 9445204774

for Excellence in Mathematics

http://www.magicmaths.org

R ORM

LongOverdue

A Genuine

TN Textbook

Formula Factory

Put MA

THSBAC

KONTRACK

SavetheChildren

&

MATHEMATICS!


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Formula Factory (TAMILNADU STATE BOARD TEXT-BOOK STD VIII - 2011-12)

2

The 9-member (Text-Book) Committeeof Tamilnadu

that prepared the above text-book has really done

A great service to the entire humanity.

They have successfully invented/identified38 Rules and Formulae.

So that VIII Standard children may easily and instantly calculate

C.P., S.P., M.P., L.P.,

PROFIT/GAIN, LOSS, PROFIT/GAIN PERCENTAGE, LOSS PERCENTAGE,

SIMPLE INTEREST,

COMPOUND INTEREST FOR FRACTIONAL PERIODS LIKE 3

YEARS

(INTEREST BEING COMPOUNDED HALF-YEARLY) ETC. ETC.

By Mugging up these 38 results

The children will get All the Life skillsneeded andlive happily for the rest of their lives.

What a mighty contribution to Society & Mathemataics

Our ELDERSwho were not that smart after all,

used only 2 formulaenamely

Simple interest =

P n r

100

Compound Interest

Amount at the end of nth year is A = P

nr

1100

THANK YOU

for these

38Formulaeto

MEMORISE

Chapter 3: Life MathematicsPercentage, Application to Profit, Loss, Interest


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3

3.2 Revision: Profit, Loss and Simple Interest Pages 95 - 96

RESULTS ON PROFIT, LOSS AND SIMPLE INTEREST

(i) Profit or Gain = Selling price Cost price

(ii) Loss = Cost price Selling price

(iii) Profit % =Profit

x 100C.P.

(iv) Loss % =Loss

x 100C.P.

(v) Simple Interest (I) =

Principal x Time x Rate

100 =

Pnr

100(vi) Amount = Principal + Interest

Example 3.5

... ... ...

Remember

Percentage of increase = Increase in amount x 100Original Amount

Percentage of decrease =Decrease in amount

x 100Original Amount

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4

3.3.2 Application of Profit and Loss Pages 99 - 100(i) Illustration of the formula for S.P.

Consider the ... ...

S.P. = C.P. + Profit... ... ...

Selling price (S.P.) =(100 + Profit %)

x C.P.100

(ii) Illustration of the formula for S.P.

Consider the ... ...

We know S.P. = C.P. + Profit

... ... ...

C.P. = 100 x S.P.(100 + Profit %)

We now summarize the formulae to calculate S.P. and C.P. as follows:

1. When there is profit 1. When there is a loss

(i) C.P. =100

x S.P.

(100 + Profit %)(i) C.P. =

100x S.P.

(100 - Loss %)

2. When there is profit 2. When there is a loss

(ii) S.P. =(100 - Loss %)

x C.P.100

(ii) S.P. =(100 - Loss %)

x C.P.100

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5

3.3.4 Application of Discounts Pages 105-108

Discountis the reduction on the Marked Priceor List Price of the article.

The normal pricr attached to the article before the discountmade is called as Marked Price (M.P.) or List Price of the article.

... ... ...

Hence we conclude the following:

Discount = Marked Price Selling Price

Selling Price = Marked Price Discount

Marked Price = Selling Price + Discount

Example 3.13

[After a tedious solution, a formula-method is offered as a better option. - Prof. Doss]

M.P. =100

x S.P.(100 - Discount %)

Example 3.14


M.P. =100 + Gain%

x C.P.(100 - Discount %)

Example 3.15


C.P. =(100 - Discount %)

x M.P.100 + Gain%

+4Formulae

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6

3.3.5 Application of Tax Pages 109-116

... ... ...

Calculation of Sales Tax

Amount of Sales Tax = Rate of Sales Tax x Cost of the item100

Rate of Sales Tax =Amount of Sales Tax

x 100Cost of the item

Bill Amount = Cost of the item + Amount of Sales Tax

3.4 Compound Interest

... ... ...

Simple interest =P x n x r

100

Compound Interest

Amount at the end of nth year is A = P

nr

1100

C.I. at the end of n yeas is given by A P

(i.e.) C.I. = P

nr

1100

P

To Compute Compound Interest

Case 1: Compunded Annually

Here A = P

nr

1100

and C.I. = A P

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7

Compound Interest Page 117

Case 2: Compunded Half-Yearly (Semi-Annually)

When the interest is compounded Half-Yearly, there are two conversion

periods in a year each after 6 months. In such sitations, the Half-Yearly rate

will be half of the annual rate, that isr

2

.

In this case, A = P

2n

1 r1

2 100

and C.I. = A P

Case 3: Compunded Quarterly

When the interest is compounded quarterly, there are four conversion

periods in a year and quarterly rate will be one-fourth of the annual rate,

r

4

In this case, A = P

4n

1 r1

4 100

and C.I. = A P

Case 4: Compunded when time being fraction of a year

When interest is compounded annually but ime being a fraction.

In this case, when interest is compounded annually but time being a fraction

of a year, say 5

1

4 years, ten amount A is given by

A = P

5r 1 r

1 1100 4 100

and C.I. = A P

for 5 years for1

4year

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3.5 Difference between Simple Interest and Compound Interest Pages 120

When P is the Principal, n = 2 years and r is the Rate of interest,

Difference betweeen C.I. and S.I. for 2 years = P

2r

100

3.5.1 Appreciation and Depreciation

a) Appreciation A = P

nr

1100

b) Depreciation A = P

nr

1100

3.6 Fixed Deposits and Recurring Deposits

Tofindthe formula for calculating interest and the maturity amount for R.D:

Let r% be the rate of interest paid and P be the monthly instalment paid for n monthsl

Interest =PNr

100, where N =

1 n(n 1)

12 2

years

Total Amount due at maturit is A = Pn +PNr

100

3.6.1 Hire Purchase and Instalments

Equated Monthly Instalmen (E.M.I.)

E.M.I. =Principal + Interest

Number of months

Example 3.5 ... ... ...

Monthly Instalment =Total amount

Number of months

+7Formulae

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