Algebraic expressions-help

write as a algebraic expression: the number of days in x weeks?? and 90% of what number is 45? I came up with 405??

The number of days in x weeks = 7x

You might want to write it as something like d = 7x ... but make sure you define "d".

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You could think of it this way. (This is how I'd work it out in my head.)

90% of x = 45
10% of x = 45/9 = 5
100% of x = 5 * 10 = 50

The unknown number is 50. (90% of 50 is 45.)

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If 7 equals the number of days in a week and n equals the number of days in the amount of weeks and x equals the number of weeks than an equation would be:

7 *x (* means multiply) = n it could also be: 7x = n. (a number by a variable means to multiply) So if the amount of weeks was 89 it would be:
7* 89 = 623

In words the equation is 7 multiply by amount of weeks will equal amount of days in the amount of weeks.


If 90% is the decimal number 0.9 and n is the number that 90% of is 45 than the equation is:

0.9n = 45 (Of in math typically means multiply. Is means equals, so literally 90% multiplied by n will equal 45)

To find what the variable(n) equals you use opposite operation to isolate the variable: If the equation uses multiply you use division to solve:

0.9n = 45 First you divide 0.9n by 0.9 and get 1n. Anything times 1 equals 1 so you can drop the 1.

Whatever you do to one side of the equation you have to do to the other ( you need to equalize the equation)

So you divide 45 by 0.9 which equals 50.

So your equation now looks like this : n = 50.

So 90% of 50 is 45.

0.9 * 50 = 45 :)

Sorry for the long answer...

1.) In one week, there are seven days. In two weeks, there are fourteen days. That means that to get the number of days in x weeks, you multiply by 7, which is 7x days in x weeks.

2.) 90% of what is 45?
Rewrite as a multiplication problem:
.9*x = 45
Divide by .9:
.9x/.9 = 45/.9
x = 50

1).
1 week = 7 days
The number of days in x weeks:
7x days

2).
90% of what number is 45?
90% of 50 is 45.