Topic: sums list of topics
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11 items are filed under this topic.

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	Odds and evens in an n by n+1 table		2010-01-21
		From Shankar: The boxes of an n * (n+1) table ( n rows and n+1 columns) are filled with integers. Prove that one can cross out several columns ( not all of them !) so that after this operation all the sums of the numbers in each row will be even. Answered by Robert Dawson.
	The distribution of sample sums		2008-11-21
		From Mark: For large samples, the sample sum (Σ x) has an approximately normal distribution. The mean of the sample sum is n*μ and standard deviation is (σ*√n). The distribution of savings per account for savings and loan institution has a mean equal to $750 and a standard deviation equal to $25. For a sample of 50 such accounts, find the probability that the sum in the 50 accounts exceeds $38,000. Answered by Penny Nom.
	T-totals		2007-09-26
		From Asma: I wanted to know what i should include in my T-totals maths coursework and also how i should lay out the coursework? Answered by Penny Nom.
	Two groups that have equal sums		2005-09-30
		From Anita: using the numbers 1, 2, 3, 4, 5, 6, 7,and 8. how do we divide them into two groups so that they have equal sums? Answered by Penny.
	Adding consecutive integers		2005-05-13
		From Yas: i need some help with my work which is to investigating sums of consecutive numbers for example: 15= 4+5+6 and 15=1+2+3+4+5 Answered by Penny Nom.
	Two matrix problems		2005-03-30
		From Sue: Question 1 Suppose all matrices in the equation below are square and invertible. Solve for x . BA-1XB-1 + 2BA + In = 0 (the symbol "0" here denotes the matrix of all 0's in it) Also, A-1 or B-1 is indicating inverse and "In" = for example, A-1 times A I hope you understand the above. I have to show all the steps. Question 2 Suppose we consider the set of all 2x2 matrices along with the operations of matrix addition and multiplication. Do they form a field? Why or why not? I think the answer is no because under multiplication it is not commutative and not all square matrices are invertible. I not positive so I'd like some help. Answered by Penny Nom.
	A matrix construction problem		2005-03-14
		From Marcelo: I want to know if is it possible to solve this problem: I have an empty NxM matrix and I know totals (sum) by rows and totals by column. Is there any algorithm to fill the matrix so that the summary of columns and rows gives the original values I have? Answered by Harley Weston.
	Sums and differences		2004-02-10
		From David: The sum of two whole numbers is 63. The difference between the numbers is 10. Find all the possible pairs. Answered by Claude Tardif and Penny Nom.
	Sums of evens		2002-09-14
		From Rosa: How do I find a geometric way to easily compute sums of consecutive even numbers 2 + 4 + 6 + .... Answered by Leeanne Boehm and Harley Weston.
	A dollar, quarter, dime, nickle and penny		2001-01-07
		From Sarah: Arnold has a dollar coin, one dime, one quarter, one nickel, and a penny. The number of different sums of money that can be formed using three coins is... Answered by Penny Nom.
	Riemann sums		2000-03-30
		From Joshua D. Parham: If n is a positive integer, then lim (1/n)[1/(1+1/n) + 1/(1+(2/n) + ... + 1/(1+n/n)] n->infinity can be expressed as the integral from 1 to 2 of 1/x dx Answered by Penny Nom.

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