Question 123

Out of four numbers, the average of the first three is 15 and that of the last three is 16. If the last number is 19, the first is

Solution

Let the 4 numbers be $$a,b,c,d$$ and $$d = 19$$

Average of first three numbers = 15

Sum of first three numbers = 3*15 = 45

=> $$a + b + c = 45$$

Sum of last three = 3*16 = 48

=> $$b + c + d = 48$$

=> $$b + c = 48 - 19 = 29$$

Substituting in above equation, we get :

=> $$a + 29 = 45$$

=> $$a = 16$$

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