Page 92 - Maths Skills - 7

90 Maths

Let’s Attempt

Example 1: A man spends 85% of his monthly salary. If he saves ` 900 per month, what is his monthly salary?
Solution: Let the salary be ` 100.
Then he spends = ` 85.
\ His saving is ` (100 – 85) = ` 15.

If the saving is ` 15, then salary is ` 100.
If the saving is ` 900, then salary is ` 100 × 900 = ` 6000.
15
Hence, his monthly salary is ` 6000.

Example 2: The price of a cellphone reduced from ` 3500 to ` 3100. What percentage is the decrease from its
original price?

Solution: Decrease in price = ` (3500 – 3100) = ` 400.
3
Percentage decrease of ` 400 on ` 3500 is 400 × 100 = 11 %
3500 7
 Decreased value 
Or, we know that decrease % =  ×100 
 Original value 

 400 
=  3500 × 100 [Q Decrease = ` 400, and Original value = ` 3500]



3
\ Decrease = 11 % .
7
Example 3: In an entrance examination 80% of the candidates passed and 60 failed. How many candidates
appeared?
Solution: Let the number of candidates that appeared be x.

Pass percentage of the candidates = 80%
Fail percentage of the candidates = (100 – 80)% = 20%
Then, 20% of x = 60
20 60 × 100
Or, × x = 60 ⇒ x = = 300
100 20
Hence, 300 candidates appeared for the entrance examination.

Example 4: Amit got 70% marks out of 500. How many more marks are needed to secure 90%?
Solution: Amit got 70% marks out of 500.
70
\ Marks obtained by Amit = 70% of 500 = 100 × 500 = 350
If Amit got 90% marks out of 500, then
90
Marks obtained by Amit = 90% of 500 = × 500 = 450
100
\ Amit needs (450 – 350) = 100 marks more to secure 90%.

Example 5: The marked price of an article increases from ` 15 to ` 21. What is the percentage increase in the
marked price of the article?
Solution: Difference in marked price = ` 21 – ` 15 = ` 6.