Difference between revisions of "1971 AHSME Problems/Problem 16"

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If we add <math>18</math> to the first <math>35</math> numbers, the new average is <math>\frac{648}{36} = 18</math> still.
 
If we add <math>18</math> to the first <math>35</math> numbers, the new average is <math>\frac{648}{36} = 18</math> still.
  
The two averages are the same, therefore the answer is <math>\textbf{(A) }1:1.</math>
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The two averages are the same, therefore the answer is <math>\boxed{\textbf{(A) }1:1}.</math>
  
 
-edited by coolmath34
 
-edited by coolmath34
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== See Also ==
 +
{{AHSME 35p box|year=1971|num-b=15|num-a=17}}
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{{MAA Notice}}

Latest revision as of 08:00, 5 August 2024

Problem

After finding the average of $35$ scores, a student carelessly included the average with the $35$ scores and found the average of these $36$ numbers. The ratio of the second average to the true average was

$\textbf{(A) }1:1\qquad \textbf{(B) }35:36\qquad \textbf{(C) }36:35\qquad \textbf{(D) }2:1\qquad  \textbf{(E) }\text{None of these}$

Solution

Assume the $35$ scores are the first $35$ natural numbers: $1, 2, 3, \dots 35.$

The average of the scores is $\frac{\frac{(35)(36)}{2}}{35} = 18.$

If we add $18$ to the first $35$ numbers, the new average is $\frac{648}{36} = 18$ still.

The two averages are the same, therefore the answer is $\boxed{\textbf{(A) }1:1}.$

-edited by coolmath34

See Also

1971 AHSC (ProblemsAnswer KeyResources)
Preceded by
Problem 15
Followed by
Problem 17
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
All AHSME Problems and Solutions

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