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liberstina [14]
3 years ago
5

Sixty percent of students in Mariana's class has a pet. If 12 students have pets, how many students are in the class

Mathematics
1 answer:
Likurg_2 [28]3 years ago
6 0
20 students, because 12 is 60% of 20.
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The set of the consecutive odd numbers 1, 3, 5, 7, ... , N has a sum of 400. How many numbers are in the set?
Amanda [17]

Well, we could try adding up odd numbers, and look to see when we reach 400. But I'm hoping to find an easier way.

First of all ... I'm not sure this will help, but let's stop and notice it anyway ...
An odd number of odd numbers (like 1, 3, 5) add up to an odd number, but
an even number of odd numbers (like 1,3,5,7) add up to an even number.
So if the sum is going to be exactly 400, then there will have to be an even
number of items in the set.

Now, let's put down an even number of odd numbers to work with,and see
what we can notice about them:

         1, 3, 5, 7, 9, 11, 13, 15 .

Number of items in the set . . . 8
Sum of all the items in the set . . . 64

Hmmm.  That's interesting.  64 happens to be the square of 8 . 
Do you think that might be all there is to it ?

Let's check it out:

Even-numbered lists of odd numbers:

1, 3                                   Items = 2, Sum = 4
1, 3, 5, 7                           Items = 4, Sum = 16
1, 3, 5, 7, 9, 11                 Items = 6, Sum = 36
1, 3, 5, 7, 9, 11, 13, 15 . . Items = 8, Sum = 64 .

Amazing !  The sum is always the square of the number of items in the set !

For a sum of 400 ... which just happens to be the square of 20,
we just need the <em><u>first 20 consecutive odd numbers</u></em>.

I slogged through it on my calculator, and it's true.

I never knew this before.  It seems to be something valuable
to keep in my tool-box (and cherish always).


3 0
3 years ago
A right rectangular prism has a length of 6 cm, a width of 8 cm, and a height of 4 cm. The dimensions of the prism are doubled.
SVETLANKA909090 [29]
The formula for the surface area of a prism is
A = 2 (wh + wl + lh)
where A is the surface area
w is the width
l is the length
h is the height

w = 8 x 2 = 16
l = 6 x 2 = 12
h = 4 x 2 = 8
substitute to the given formula

A = 2 ( (16 x 12) + ( 16 x 8 ) + ( 12 x 8) )
A = 832 sq cm is the surface area of the new rectangular prism
4 0
3 years ago
Read 2 more answers
Alis needs 10 strips of ribbon each 2 and 1/2 feet. how much ribbon in all is needed
BlackZzzverrR [31]

Answer:

She needs 25 feet

Step-by-step explanation:

10 * 2.5 = 25

5 0
2 years ago
Read 2 more answers
bank offers two interest account plans. Plan A gives you 6% interest compounded annually. Plan B gives you 13% annual simple int
Murrr4er [49]
2520  hope this helps!

5 0
2 years ago
The base of a triangle is 4x+6cm,the height is 5cm. What is the actual length of the base
zavuch27 [327]
Is it 10cm long? 4 + 6 =10
5 0
2 years ago
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