SHORT CUT METHOD OF ARITHMATIC
Compound discount:
·
You can calculate compound
interest mentally
Question Find the compound interest on Rs 2500 @ 12% P.A. for two years
This method is very useful if time is in 2 units
Step 1 First we add rates Let it be A
Step 2 Multiply rates and divide by 100 Let it be B
Step 3 Add A and B It is our compound interest rate percentage for two years .Take
percentage
12 + 12 + ( 12+ 12
) = 24 + 1.44 = 25.44 Question Find the compound interest on Rs 2500 @ 12% P.A. for two years
This method is very useful if time is in 2 units
Step 1 First we add rates Let it be A
Step 2 Multiply rates and divide by 100 Let it be B
Step 3 Add A and B It is our compound interest rate percentage for two years .Take
percentage
100
Find 25.44 % of 2500 and that is compound interest
625 + 11 =636 ( Again consult lesson no1 9 for fast percentage calculations)
Rs 636 is our compound interest
Successive Discount:
·
Question Find the selling
price of a saree after two successive discounts of 20 % .If
the price of that saree is
Rs800
Conventional Method 800 x
20 =
160
800- 160 = 640
100
Rs800
Conventional Method 8
1
64
1
Total discount is 800 -512 = Rs288
Effective Discount is = 288 x 1
8
= 36 %
You can calculate it mentally .How ?
Step1 Here first we calculate effective discount . Add both discounts Let it is A
Step2 Multiply both discount and divide by 100 .Let it be B
Step3 Subtract B from A .That is our effective discount
( 20 + 20 ) - ( 2
1
Now find 36%of Rs 800
= 320 - 32 =288 How? For fast percentage calculations see Lesson no 19 &20
Selling price 800 - 288 = Rs 512
Question If a trader gives 20 % retailer margin and 3 % cash discount , find the total effective discount?
20 + 3 - 20 x 3
100
23 - .6 = 22. 4 %
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