Question
Out of four numbers, the average of the first three is
16 and that of the last three is 14. If the last number is 17, then find the first number?Solution
Let the four numbers be a, b , c and d. (a + b + c)/3 = 16 (a + b + c) = 48 ----- (i) (b + c + d)/3 = 14 (b + c + d) = 42 ----- (ii) Given that last number is 17 i.e. , d = 17, now putting this value in (ii) (b + c +17) = 42 (b + c) = 42-17 (b + c) = 25 ----- (iii) Now, putting value of (iii) into (i), (a + b + c) = 48 a + 25 = 48 a = 48-25 = 23 therefore, the first number is 23.
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