Math Is Fun Forum

medianandmode

Member

Registered: 2010-01-06

Posts: 6

Urgent! average help

I have the numbers 94, 87, 90, 89.  What number would be the number that makes the average 91? thanks!:)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Urgent! average help

Hi medianandmode;

Think of it like this, for the mean to be 91, the sum of the 5 numbers would have to be 455, do you see why? The sum of 94,87,90,89 is 360. 455 - 360 = 95 so the next value has to be 95.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

medianandmode

Member

Registered: 2010-01-06

Posts: 6

Re: Urgent! average help

No, help me?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Urgent! average help

Hi;

The average or mean of five numbers is (a + b + c + d + e) / 5. Now just ask what do a+b+c+d+e have to equal so that (a + b + c + d + e) / 5 = 91?

(a + b + c + d + e) / 5 = 91 Times both sides by 5

(a + b + c + d + e)  = 5* 91 = 455

So (a + b + c + d + e)  must equal 455

say

a=94
b=87
c=90
d=89
e =?

Now just plug in:

94 + 87 + 90 + 89 + e = 455 Solve for e, the one you need to add to your list

e = 95

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

medianandmode

Member

Registered: 2010-01-06

Posts: 6

Re: Urgent! average help

thanks

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Urgent! average help

Hi medianandmode;

Glad to help. Do you understand it better now? Enough that you can do them on your own?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.