বিসিএস প্রিলিমিনারি সাধারণ বিজ্ঞান গতি

Example 21:
Bijoy spend his money from his saving in different way that is he spends 30% on travel,10% on food,15% on wages and 22% on purchase a bike and after that all expenditure he saved 4600.Find the how much he spent on bike.
Answer :
Let the total income of bijoy x. then total expenditure from income  X x (30%+10%+15%+22%)=X x 77% =Total savings= X x 23%
X = 4600 x 100 / 23 = 20000 and expenditure on Bike = 22% so,20000 x 22 / 100 = 4400.

Shortcut Tricks
The total income as 100% so ,(100% – 30%+10%+15%+22%) = 77% and now (100% – 77% ) = 23%
Bike Expenditure is now 4600 x 22 / 23 = 4400.

Example 22:
If X is 80% of Y, then What percent of X is Y ?
Solution :
X = 80 / 100 x Y
X = 4 / 5 x Y
Y / X = 5 / 4.

Example 23 :
54.5% of 600 + 30.5% of 1800 = (?) + 147
Answer :
327 + 549 = (?) + 147
(?) = 729
? = 27.

Example 24 :
What is 25% of  25% equal to ?
Answer :
25%  of 25% = 25 / 100 x 25 / 100 = 1 / 16 = 0.0625.

Example 25:
Subtracting 60% of a number from the number, We get the result as 20. The number is :
Solution :
Let the number is x, then ,
x – 60 / 100x = 20
x – 3 / 5 = 20
2x / 5 = 20
x = 20 x 5 / 2 = 50.

Example 26 :
In Mumbai due to reduction by 10% in the price of sugar , a person is able to buy 2kg more for Tk . 280 . Find the reduced rate/kg of sugar ?
Answer :
10% of 280 is due to reduction of price in sugar
Rs . 28 = 2kg
Tk . 14 = 1kg.

Example 27:
In an party election between two candidates, one got 45% of the total valid votes, 20% of the votes were invalid. If the total number of votes was 7500, the number of valid votes that the other candidate got, was
Answer :
Number of valid votes
= 80% of 7500
= ( 80 / 100 ) x7500 = 6000.
one got 45% of the votes
So other Valid votes polled by other candidate = 55% of 6000
= (55/100)×6000 = 3300.
the number of valid votes that the other candidates got is 3300.

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