Example 1:
If the difference between 45% of a number and 3/5th of that number is 18. What is the number?
Solution:
Let the number be a .
Then a x 45% – a x 3/5 = 18
a x 45% – a x 60% = 18 ∴( 60% = 3/5 )
a x 15% =18
a = 100×18 = 1800/15 = 120
Tricks:
we know 3/5 = 30%
45% – 30% = 15 %
15% = 18 = 120
Example 2:
Find the missing term
? % of 35 = 672
Answer :
Let x % of 35 = 672
Then, (x / 100) of 35 = 672
672 x 100 =67200 / 35 = 1920
Example 3:
Sixty-five percent of a number is 21 less than four-fifth of that number. What is the number?
Solution:
Let the number be Y.
Then, 4 / 5 Y -( 65% of Y ) = 21
4 / 5 Y – 65 / 100Y = 21
15Y = 2100
Y = 140.
Example 4 :
In expressing a length 81.472 Km as nearly as possible with three significant digits , Find the percentage error.
Solution :
Error = ( 81.5 – 81.472 )Km = 0.028.
So Required percentage = ( 0.028 /81.472 X 100 )% = 0.034%.
Example 5 :
The ratio 6 : 4 expressed as a percent equals to as.
Solution :
6 : 4 = 6 / 4
6 / 4 = (6 / 4 x 100 )%
= 150%
Example 6 :
Evaluate the Example ?
25% x 280 + 24% x 750
Solution:
25 / 100 x 280 + 24 /100 x 750
70 + 180 = 250
Example 7 :
A Nokia dealer sold a smart phone at 15% discount on print rate . If the customer paid Rs , 8500 and the printed price is 25%more than its cost price , What is the cost price of smart phone ?
Answer :
Cost price of smart phone = 8500 x 100 / 85 x 100 / 125
=85000000 / 10625 = 8000 .
Example 8 :
The difference between 60% of a number and 30% of the same number is 24500 . What is 75% of that number ?
Answer :
difference between 60% of a number and 30% of the same number is 24500
60% – 30% = 24500
30% = 24500
24500 x 100 / 30
So , 75% of that number is = 24500 x 75 / 30
= 2450 x 25 = 61250 .
Example 9 :
Evaluate the Example ?
58% of 30102 – 32% of 17344
Answer :
17459.16 – 5550.08 = ?
? = 11909.08
Example 10 :
Evaluate the Example ?
52% of 8540 + 15% of 7860 = ? + 2540
Answer :
4440.8 + 1179 = ? + 2450
5619.8 – 2540 = ?
? = 3079.8
এই লেকচারের পরের পেইজে যেতে নিচের 
…. তে ক্লিক কর।