বিসিএস প্রিলিমিনারি সাধারণ বিজ্ঞান গতি

Example 11:
Bibhas work in shop and his 30% of income is  Rs.1800 . Now Find the 65% of his income and also find the 1 / 5 of Bibhas income .

• Solution: 30% = 1800 So, 65% = 1800 x 65 / 30 = 3900

• Shortcut Trick: 1800 x 65 / 30 = 3900.

• Solution: we know that 1 / 5 = 20% so, 1800 x 20 / 30 = 1200.

Example 12:
Bibhas ‘s salary was decreased by 20% and subsequently increased by 20%, How much percent does he lose?
Solution:
Let Bibhas’s original salary = Rs.100
Now salary  is = 120% of 20% of 100 = 150 / 100 x 80 / 100 x 100 = 24.
So, Bibhas Decrease salary is = 4%

Example 13:
If the sum of 40% & 20% of a number is 425 . Find the 75% of that number ?
Answer :
40% + 20% = 520
60% = 520
1% = 520 / 60
75% = 520 x 75 / 60 = 650

Example 14:
Karan’s monthly income is Rs. 14000 . If his monthly income is increased by 10% . Find the total income after 2 months ?
Solution :
= 14000 x 110 x 110 / 100 x 100
= 16940
Example 15:
Jamal’s salary is increased by 10% & he got now Rs. 6000 . Find the salary before the increase ?
Answer :
6000 x 100 / 110 = 5454.54

Example 16:
If  the product of 15% & 20% of a number is 360 . Find the sum of the 15% and 20% of that number ?
Answer :
15% x 20% = 360
300% = 360
1% = 360 / 300
Sum of ( 15 + 20 )% = 35%
35% = 360 x 35 / 300 = 42.

Example 17:
If Rahul’s income is 20% more than Rohan then how much % Rohan’s income is less than that of Rahul’s income ?
Answer :
We applied formula = ( increment% / 100 + increment% ) x 100
20 / 100 + 20 = 20 x 100 / 120 = 50 / 3

Example 18:
Falguni’s salary is 40% of Dipika salary which is 25% of Rima’s salary . What percentage of Rima’s salary is Falguni’s salary ?

Answer :
Falguni : Dipika : Rima = 40 : 100 : 400
= 2 : 5 : 20
So , Required percent = 2 x 100 / 20 = 10%

Example 19:
Nilam who invest 25% of her income and she is able to save Rs.1500 per month.How much money her monthly expenses (in Rs.) :
Solution :
Let her monthly income be Rs. X
Then ( 100 – 25)% of X = 1500
(75 % of X) = 1500
(75 /100) x X = 1500
X = 1500 x 100 / 75
X = 2000
Monthly expenses is = Rs.(2000 – 1500) = Rs. 500

Example 20:
If X = p % of q and Y = q % of p, then which of the following is true?
a)X is smaller than Y.
b)Relation between X and Y cannot be determined.
c)If p is smaller than q,then X is greater than Y.
d)None of these.
Answer :
p % of q = p x q / 100
q % of p = q x p / 100
So, X = Y
So both are equal.
Ans : d.

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