The Small One

10 distinct integers from the set { 1 , 2 , , 100 } \{1, 2, \ldots, 100\} are chosen and their sum is 954. What is the smallest of these 10 numbers?


The answer is 90.

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14 solutions

Victor Loh
Oct 27, 2013

The maximum sum of 10 distinct numbers chosen from 1 to 100 is 91+92+...+99+100 = 955.

For sum to be 954, the numbers chosen must be 90, (92,93,...,99,100).

Hence, the smallest number in the group is 90.

Can you explain why

For sum to be 954, the numbers chosen must be 90, 92, 93, ... , 100

How do you know that there are no other ways?

Note: The fact that this set is unique, is a crucial observation that is not pointed out in the other solutions.

Calvin Lin Staff - 7 years, 7 months ago

100 + 99 + 98 + 97 + 96 + 95 +94 + 93 + 92 + 90 = 954. So, the smallest number is 90

Moderator note:

Can you explain why this is the only set of numbers that can be chosen?

yes I also want to know that,

Shivanshu Siyanwal - 7 years, 10 months ago
Alvarana Elvatra
Dec 18, 2013

954/10 = (90 x 10) + 54

so, the integers must be 90's to 100

0+1+2+3+......+10 = 55

54= 55-1

so, 10 integers is = 90 + (0,2,3,4,........10) = 90, 92, 93,94,95,96,97,98,99,100

the smallest = 90

Alan Li
Oct 28, 2013

The largest possible sum of the first 9 would be 100+99+98+97+96+95+94+93+92=864

Then to find the smallest number in the set we subtract the sum of the current numbers from 954

954-864=90

Read the question carefully. Why do we care about the largest possible sum of the first 9? We're not looking for the smallest possible value of the 10th integer.

Calvin Lin Staff - 7 years, 7 months ago

why should we take consecutive number rather than any 10 random numbers .. ????

Aroona Ayub - 7 years, 7 months ago

Let's add up 91 to 100


91+92+93+.....100


= (91+100)*10/2


= 191*5


=955

Since the sum is 954, we replace 91 with 90.


Thus, the smallest number is 90

Robi Fajar Bahari
Aug 12, 2013

let the choosen numbers are a 1 , a 2 , . . . a 10 a_{1}, a_{2}, ... a_{10} where a 1 < a 2 < a 3 < a 4 < a 5 < a 6 < a 7 < a 8 < a 8 < a 9 < a 10 a_{1}<a_{2}<a_{3}<a_{4}<a_{5}<a_{6}<a_{7}<a_{8}<a_{8}<a_{9}<a_{10} . we want to find min( a 1 a_{1} ). a 1 a_{1} is minimum if and only if a 2 + a 3 + . . . + a 10 a_{2} + a_{3} + ... + a_{10} is maximum, and the maximum value of a 2 + a 3 + . . . + a 10 a_{2} + a_{3} + ... + a_{10} reach when a 2 + a 3 + . . . + a 10 = 92 + 93 + 94 + . . . + 100 = 864 a_{2} + a_{3} + ... + a_{10} = 92+93+94+...+100=864 .

so, min( a 1 = 954 864 = 90 a_{1}=954-864=90 )

Moderator note:

Note that this interpretation of the problem is incorrect. You are not asked for the smallest possible value of the smallest number (i.e. \min (a_1)), but are asked for the value of \(a_1 .

You need to explain why we must have a 1 = 90 a_1 = 90 . In fact, there is only 1 set of 10 numbers which will work for this problem. The value 954 is specially chosen. If the sum was 953, then the smallest value is not uniquely determined.

as 10 distinct integers for [1,2,.......,100],

smallest of these 10 numbers=954-100-99-98-97-96-95-94-93-92=90(the smallest)...

Marcos Oliveira
Jan 4, 2014
  • 100 + 99 +98+97+96+95+94+93+92+90 = 954

O menor é 90 \boxed{90}

Devesh Rai
Nov 2, 2013

SINCE WE EXAMINE THAT 91+92+93+94+95+96+97+98+99+100=954. SO IF WE TAKE 1 LESS NUMBER THAT IS 90 AND WHICH IS ALSO DISTINCT IN THE PLACE OF 91 WE WILL GET THE SUM = 954 AND SINCE 90 IS THE SMALLEST NUMBER SO ANSWER IS 90

Ads Hjhj
Oct 31, 2013

100+99+98+....+91=955.BUT WE WANT SUM TO BE 954.THEREFORE WE WILL SUBTRACT 1 FROM ANY ONE NUMBER.SINCE,WE ARE ASKED SMALLEST NO. WE WILL SUBTRACT 1 FROM SMALLEST NUMBER i.e. 91-1=90

Aditya Karekatte
Oct 28, 2013

The maximum possible numbers which can be selected are 100, 99, 98, 97, 96, 95, 94, 93 and 92. Subtracting the sum of these from 954, we get \boxed{90}

Sam Leo
Oct 28, 2013

x+100+99+98+..+92 = 954, where x is the smallest number possible. (The other 9 distinct numbers have to be as large as possible for x to be the smallest.)

100+99+98+..+92 = 864 Therefore, x = 954-864 = 90 .

Note that we are not asking for the smallest possible value of x x , which would then justify saying that the other 9 numbers must be as large as possible.

There is something more subtle that is happening in this question.

Calvin Lin Staff - 7 years, 7 months ago
Subham Biswas
Aug 14, 2013

"n"be a number then it will n,n+1,n+2,n+3.......,n+10...now if we add them it would be 10n+45....it should be equal to 954.......then after solving it comes out to be 90. something ...so it should be 90....

Moderator note:

It is not a valid assumption that the numbers are consecutive.

90 something is not 90.

In this case, it is impossible if the 10 numbers are less than 90.

100 + 99 + 98 + 97 + 96 + 95 + 94 + 93 + 92 + 91 = 955. (1 more than the sum).

If we change 91 with 90, then:

100 + 99 +98 + 97 + 96 + 95 + 94 + 93 + 92 + 90 = 954

Thus, the answer is 90.

Moderator note:

How do you know that there are no other sets of 10 numbers which satisfy the conditions?

we know because if only this set of numbers bring the required sum....any other set with reqwuired assumptions of distinct numbers would bring up a number less than 954.

Nabasindhu Das - 7 years, 9 months ago

Let us find the maximum possible sum that can achieved with 10 distinct numbers less than 100. We have 100+99+98+97...=955. As we are asked to find the set in which sum is 954 that means one of the numbers in our set should be decreased by 1 and also should be distinct. And the only possible case is when 90 is lowest.

Abhishek SETHI - 7 years, 9 months ago

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