Math Is Fun Forum

tianabasu

Member

Registered: 2008-03-20

Posts: 1

Arithmetic mean!

Please help me by solving the below mentioned questions, i have got stuck with.  regards,

Q1) There are 45 students in the class, of which 15 are girls.  The mean weight of girls is 42 kg and that of boys is 48 kg.  Find the mean weight of the entire class.

Q2) The mean 40 numbers was found to be 38.  Later on, it was detected that a number 56 was misread as 36.  Find the correct mean of the given numbers.

luca-deltodesco

Member

Registered: 2006-05-05

Posts: 1,470

Re: Arithmetic mean!

there are 45 students, 15 of which are 42kg, and (45-15=30) of which are 48kg

when you find the mean you add up all the numbers and divide by the number, since you are finding mean weight, you add up all the weights which is and divide by 45 which is:

(15×42 + 30×48)÷45 = 46

..........

you have 40 numbers, with mean 38. you then have the new set of numbers which is in total, 20 more than the previous sum.

so lets say the sum of the original 40 numbers is 't' you have t÷40 = 38.
with the new set of numbers you have (t+20)÷40 = t÷40 + 20÷40 = 38 + ½ = 38½

--- made corrections

Last edited by luca-deltodesco (2008-03-20 21:43:06)

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JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: Arithmetic mean!

No, Luca. The actual total should be 20 more than what was calculated. The correct mean of the numbers should be 38½.

luca-deltodesco

Member

Registered: 2006-05-05

Posts: 1,470

Re: Arithmetic mean!

ah yeh, i misread the question.

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tianabasu

Member

Registered: 2008-03-20

Posts: 1

Re: Arithmetic mean!

Thank you so much for your help. :-)