The average of following 5 numbers is 8, find the missing number in 7, 5, 3,12,?.

Explanation:
Weight of A+B+C = 45  × 3 = 135 kg .....(i) 
Wt. Of A+B = 40 × 2 = 80 kg .....(ii)
Weight of B + C = 43 × 2 = 86 kg ......
(iii)
Now on adding (ii) and (iii), 
wt. of A+2B+C = 166kg
A+B+ C = 135 kg ....given (i)
On Subtracting  (i)
B = 31 kg ..Ans

Explanation:
Let the 4th number be x,
Then the average of first three numbers = 2x ,
So the sum of first 3 numbers = 2x × 3 = 6x,
Since the average of 4 numbers = 12.
Then sum of 4 numbers = 12 × 4 = 48.
so, 48 - 6x = x => 7x = 48,
x = 48/7 ..Ans.

Explanation:

Explanation:
Lets take total votes =100%            10%doesn’t cast their votes   So, (100-90) = 90% cast their votes.                       total valid votes = 90% -85 one candidate get 50% of votes of voters list.                 So, other candidate get = (90% - 85 )-50%= 40% - 85             so ,50 % - (40% - 85) = 165      50% - 40% + 85 = 165        10% = 80                           100 % = 800                      So total voters is 800 

Explanation:
Sol.  Let cp = 100,  MRP = 150

  \(  sp = 150 \times {80 \over 100} \)

  \( = Rs. 120 \)

Hence, Profit = 20%


  [short trick:]
By successive formula
\( x+y+{xy \over 100} \)

\( 50-20+{50 \times (-20) \over 100} \)
30 – 10 = 20%

Explanation:
Given, ratio is 5 : 1 that means antecedent is 5 times greater than the consequent.
Given consequent =  10, so the number is 10 ×  5  =  50 answer.

Explanation:
Given ratio of  girls : boys   = 5 : 7 = 5/7
multiplying the antecedent and consequent by the same number, let by x,
girls = 5x, and boys = 7x 
total  = 120;
as par given 5x + 7x = 120
=> x = 120/12 = 10
hence, girls  = 5 × 10 = 50 
and Boys = 7 × 10 = 70  answer

Explanation:
in a ratio the first term is called antecedent and the second term is called consequent. in 3 : 5,  3 is antecedent and 5 is consequent, means and extremes are terms used in case of proportion 
i.e. 1 : 2 :: 2 : 4, here 1 and 4 are extremes and 2 and 2 are means.