Question : The average of a, b, and c is 20, and that of b, c, and d is 25. If d = 30, then the value of a is:
Option 1: 25
Option 2: 45
Option 3: 30
Option 4: 15
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Correct Answer: 15
Solution :
The average of a, b, and c is 20, and that of b, c, and d is 25.
a + b+ c = 3 × 20 = 60 ---(i)
b + c+ d = 3 × 25 = 75 ---(ii)
Solving equations (i) and (ii),
⇒ a – d = 60 – 75
⇒ a – 30 = –15
$\therefore$ a = 15
Hence, the correct answer is 15.
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