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5 votes
One way of writing 75 as the sum of consecutive whole numbers is 24 + 25 + 26. How many other ways are there? ​

2 Answers

1 vote

Answer:

4 other ways (5 ways, total).

Explanation:

You want to know how many other ways 75 can be written as the sum of consecutive whole numbers other than 24+25+26.

Solution

If 75 is written as the sum of an odd number of integers, the middle integer of the set will be 75 divided by the number of integers. The divisors of 75 are {1, 3, 5, 15, 25, 75}. If the numbers in the sum are non-negative, the number of integers involved cannot be more than √(2·75) ≈ 12. Then allowed odd numbers of integers in the sum are 3 and 5.

If 75 is written as the sum of an even number of integers, the quotient when 75 is divided by the number of integers must be 1/2 more than a whole number. Such integer divisors are 2, 6, and 10.

Sums

37 + 38 = 75 . . . . 2 integers

24 + 25 + 26 = 75 . . . . 3 integers (the given sum)

13 + 14 + 15 + 16 + 17 = 75 . . . . 5 integers

10 + 11 + 12 + 13 + 14 + 15 = 75 . . . . 6 integers

3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 = 75 . . . . 10 integers

There are 4 other ways to use consecutive non-negative integers to make a sum of 75.

4 votes

Answer:

None.
24+25+26 is the only valid answer

Explanation:

We can create an expression for the sum of 3 consecutive numbers.


S=x+(x+1)+(x+2)

Which we can simplify to


S=x+x+1+x+2


S=3x+3

In this example we are given a sum of 75.


75=3x+3

Lets solve for
x.

Subtract 3 from both sides.


72=3x

Divide both sides by 3.


24=x

To find out what the 3 numbers are we can plug in 24 for x


x+(x+1)+(x+2)


24+(24+1)+(24+2)


24+25+26

User Aleksey Deryagin
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