Aptitude Shortcuts Method for Average Related Problems Type-I

Aptitude Shortcuts and Mind Tricks for Average Related Problems
Aptitude Shortcuts Method for Average Related Problems Type-I
Aptitude Shortcuts methods that used in aptitude questions related to Average Problems were given below in pdf. Candidates those who are preparing for SSC/FCI and all other competitive exams can use this.


Model Question:
1.) The Average Cost of 8 pens and 5 pencils is Rs. 25, and the average cost of 4 pens
and 7 pencils is Rs. 21. What is the total cost of 18 pens and 18 pencils?

Given:
Average Cost of 8 pens and 5 pencils= Rs. 25
Average Cost of 4 pens and 7 pencils= Rs. 21
Asked: the total cost of 18 pens and 18 pencils=?

Shortcut Method:
Initially we have to find the total cost of 8 pens and 5 pencils,
8 pens + 5 pencils = 25 × 13

Note: To find the total cost of the 8 pens and 5 pencils we are multiplying the average
cost and number of the pens and pencils.

So, 8 pens + 5 pencils= 325 --à equation (1)
Likewise we are calculating the total cost of 4 pens and 7 pencils,
4 pens + 7 pencils = 21 × 11
4 pens + 7 pencils = 231à equation (2)
Now we have to add Equation (1) and (2)
12 pens + 12 pencils = 325 + 231
12 pens + 12 pencils = 556

Here we got the total cost of 12 pen and 12 pencils, and in the problem they asked the
total cost of 18 pens and 18 pencils.
  
For that we are using a simple matrix method;
12 ⋯ 556
  ⋮   ⋱    ⋮
 18 ⋯   𝑥
Explanation for the above matrix method:

  • In the above matrix methods in four data one data should be unknown then only we can apply this method.
  • Here we take that, total cost of 12 pens and pencils is 556, and then what is the total cost of 18 pens and pencils.
  • Take ‘x’ as the total cost of 18 pens and 18 pencils Cross multiply the above matrix equation then we will get as,
12x= 10008
x=10008/12
x= 834
Answer= 834; the total cost of 18 pens and 18 pencils are Rs. 834


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