Question

The average weight of 9 children is 26.5 kg. When a tenth joins them , the average increases to 27 kg. What is the weight of tenth child?

Answer 1

Average weight is 26.5 when they are 9
So total weight of 9 students is= 9×26.5=238.5
Total weight of 10 students at the average of 27=27×10=270
So weight of 10th student=Total weight of 10 students at average of 27 - Total weight of 9 students at average of 26.5
=270-238.5=31.5

Answer 2

Hi ,

we know that,
_____________________________
mean
= ( sum of the observations ) /( number of
observations )
______________________________

i ) sum of 9 children weight = 9 × mean

= 9 × 26.5kgs

= 238.5 kg

ii) let weight of 10th child = x kg


sum of 10 children weight= 238.5 + x ---( 1 )

number of children = 10 -----( 2 )

new mean = 27kg

therefore ,

( 1 )/ ( 2 ) = new mean

( 238.5 + x )/ 10 = 27

238.5 + x = 27 × 10

x = 270 - 238.5

x = 31.5kg

Weight of 10 children = x = 31.5 kg

I hope this helps you.
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