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Answers by David W.

A proportion is two equal ratios.   "y is to 20 as 9 is to 5" written as ratios, this is:     y : 20  ::  9 : 5   written as fractions, this is:     y/20 = 9/5      y = 36       ...

x+4=-x-4     2x + 4 = -4             [add x to both sides]   2x = -8                   [subtract 4 from both sides]    x = -4   Check:   Is   (-4)...

Gauss' famous formula for the Sum of the Numbers from 1 to n is:      Sum = n(n+1)/2   Now, if you know the sum, for example, 1953, this is:      1953 = n(n+1)/2      3906 = n2 + n       ...

Let x = the what   Translate: "9 divided by what equals 16"   9      /       x          =     16    9 = 16x                    ...

"three consecutive integers" Let them be x, (x+1), and (x+2).   "the difference between three times the largest and two times the smallest integer is 30"   means                        ...