To find an average of quantities of the same kind is to add all the items together and then divide the sum by the number of items.
Average = sum of all items/ No. of items
( Average = {sum of all items over No. of items} )
Practice these questions below using this formula.
Practice Problems on Average | Math Quiz
Q1. The average weight of A, B and C is 45 kg, that of A and B is 40 kg and B and C is 43 kg. What is the weight of B?
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
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
Q2. The average of following 5 numbers is 8, find the missing number in 7, 5, 3,12,?.
The sum of all numbers = 8 × 5 = 40
So, ? = 40 - (7+3+12+5) = 13 Ans.
So, ? = 40 - (7+3+12+5) = 13 Ans.
Q3. The average of the first three numbers is double of the fourth number. if the average of all the four numbers is 12, find the 4th number.
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.
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.
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