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lora16 [44]
3 years ago
5

Five students wrote a mathematics test. The average mark was 68. If the marks for four of the students were 75, 62, 84 and 53, t

he mark of the fifth student was
Mathematics
1 answer:
konstantin123 [22]3 years ago
4 0

Answer:

66

Step-by-step explanation:

Use the formula for the mean of a set of numbers:

                  sum of the numbers

average = --------------------------------

                     count of numbers

Here we know that the average mark was 68, so we can write:

               

                           75 + 62 + 84 + 53 + x

average = 68 = ----------------------------------

                                           5

or                            274 + x

                  68 = -------------------

                                    5

Solving for x, we multiply both sides by 5:     340 = 274 + x.

Subtracting 274 from both sides effectively isolates x:

 340 = 274 + x

- 274    -274

------------------------

  66      =    x

The fifth student's mark was 66.

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The first equation comes from the perimeter formula. Since it is a rectangle, there are two lengths and two widths, which must all be added to get the perimeter.  The second equation shows that the length is equal to the width plus three.  In order to solve this equation, the substitution method should be used, since the one equation is already set equal to one of the variables (L)

2l+2w=24
l=3+w

2(3+w)+2w=24
Use distributive property to get rid of the parentheses
2(3+w)+2w=24
2(3)+2(w)+2w=24
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Simplify like terms on the left side of the equation
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Divide each side by four to find the value of one w
4w/4=18/4
w=4.5
Plug 4.5 into the one equation to find the value of l
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Put the numbers into the first equation and simplify:
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15+9=24
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Answer:

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