Some Basic Formulas:1. (a + b)(a – b) = (a2 – b2)

2. (a + b)2 = (a2 + b2 + 2ab)

3. (a – b)2 = (a2 + b2 – 2ab)

4. (a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca)

5. (a3 + b3) = (a + b)(a2 – ab + b2)

6. (a3 – b3) = (a – b)(a2 + ab + b2)

7. (a3 + b3 + c3 – 3abc) = (a + b + c)(a2 + b2 + c2 – ab – bc – ac)

8. When a + b + c = 0, then a3 + b3 + c3 = 3abc.

Simplification:

Rule of ‘BODMAS’: This BODMAS rule depicts the correct sequence in which the operations are to be executed, so as to find out the value of given expression. Full form of BODMAS is B – Bracket, O – of, D – Division, M – Multiplication, A – Addition and S – Subtraction. Thus, while solving or simplifying a problem, first remove all brackets, strictly in the order (), {} and ||. After removing the brackets, we will use the following operations strictly in the following order: (i) of (ii) Division (iii) Multiplication (iv) Addition (v) Subtraction.

Average:

Average = (Sum of observations/Number of observations)

Suppose a train covers a certain distance at x kmph and an equal distance at y kmph. Then, the average speed of train during the whole journey is kmph (2xy/x+y)kmph.

Percentage:

By a certain percent, we mean that many hundredths. Thus, x percent means x hundredths, written as x%. To express x% as a fraction: We have, x% = x/100

To express a/b as a percent: We have, a/b = (a/b x 100)%

Percentage Increase/Decrease: If the price of a commodity increases by R%, then the reduction in consumption so as not to increase the

expenditure is: [(R/(100+R)) x 100]%. If the price of a commodity decreases by R%, then the increase in consumption so as not to decrease the expenditure is: [(R/(100-R)) x 100]%.

Result on Population: Let the population of a town be P now and suppose it increases at the rate of R% per annum, then: population after n years = P (1+(R/100))n Population n years ago= P/ (1+(R/100))n

Result on Depreciation: Let the present value of a machine be P. Suppose it depreciates at the rate of R% per annum. Then: Value of the machine after n years = P (1-(R/100)n , Value of the machine n years ago = P/ (1-(R/100)n, If A is R% more than B, then B is less than A by [(R/(100+R)) x 100] %, If A is R% less than B, then B is more than A by [(R/(100-R)) x 100] %

Ratio:

The ratio of two quantities a and b in the same units, is the fraction  and we write it as a : b. In the ratio a : b, we call a as the first term or antecedent and b, the second term or consequent. Eg. The ratio 5 : 9 represents 5/9 with antecedent = 5, consequent = 9.

Rule: The multiplication or division of each term of a ratio by the same non-zero number does not affect the ratio. Eg. 4 : 5 = 8 : 10 = 12 : 15. Also, 4 : 6 = 2 : 3.

Proportion:

The equality of two ratios is called proportion. If a : b = c : d, we write a : b :: c : d and we say that a, b, c, d are in proportion. Here a and d are called extremes, while b and c are called mean terms. Product of means = Product of extremes. Thus, a : b :: c : d  (b x c) = (a x d).

Simple Interest:

Principal: The money borrowed or lent out for a certain period is called the principal or the sum.

Interest: Extra money paid for using other’s money is called interest.

Simple Interest (S.I.): If the interest on a sum borrowed for certain period is reckoned uniformly, then it is called simple interest. Let Principal = P, Rate = R% per annum (p.a.) and Time = T years. Then Simple Interest = (P x R x T)/100

Profit and Loss:

Cost Price: The price, at which an article is purchased, is called its cost price, abbreviated as C.P.

Selling Price: The price, at which an article is sold, is called its selling prices, abbreviated as S.P.

Profit or Gain: If S.P. is greater than C.P., the seller is said to have a profit or gain.

Loss: If S.P. is less than C.P., the seller is said to have incurred a loss.

Gain = (S.P.) – (C.P.)

Loss = (C.P.) – (S.P.)

Loss or gain is always reckoned on C.P.

Gain Percentage: (Gain %) = (Gain x 100) / C.P.

Loss Percentage: (Loss %) = (Loss x 100) / C.P.

Selling Price: (S.P.) = [ ((100 + Gain %)/100) x C.P.]

Selling Price: (S.P.) = [ ((100 – Loss %)/100) x C.P.]

Cost Price: (C.P.)= [ (100/(100 + Gain %)) x S.P.]

Cost Price: (C.P.)= [ (100/(100 – Loss %)) x S.P.]

If an article is sold at a gain of say 10%, then S.P. = 110% of C.P.

If an article is sold at a loss of say, 20% then S.P. = 80% of C.P.

When a person sells two similar items, one at a gain of say x%, and the other at a loss of x%, then the seller always incurs a loss given by: Loss % = (x/10)2

If a trader professes to sell his goods at cost price, but uses false weights, then Gain % = [(Error/(True Wight – Error)) x 100 ]%

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