Multiple choice

The average of 1st,2nd,3rd number is 20 average of 2nd,3rd and 4th is 25. If 4th number is 25 then find value of first number?

  1. 21

  2. 29

  3. 10

  4. 17

  5. 14
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C Correct answer
Explanation

Let numbers be a, b, c, d. (a+b+c)/3 = 20 => a+b+c = 60. (b+c+d)/3 = 25 => b+c+d = 75. Given d = 25, then b+c+25 = 75 => b+c = 50. Substituting into the first equation: a + 50 = 60, so a = 10.

AI explanation

The sum of the first three numbers is 3 multiplied by 20, yielding 60. The sum of the second, third, and fourth numbers is 3 multiplied by 25, yielding 75. This means the fourth number is 15 more than the first number, since the second and third numbers cancel out when comparing the sums. Since the fourth number is 25, the first number is 25 minus 15, which equals 10.

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