Question

the average of 6 no. is 30. if the average of first four is 25 and that of the last three is 35 so waht is the 4th no,

Answer 1

$\huge\boxed{\texttt{\fcolorbox{Red}{aqua}{Hey Mate!!!}}}$

$<b><i><font face=Copper black size=4 color=blue>$ Here is your answer.
As we know the formula

Sum of all Numbers = Average ×Total Numbers

Sum of 6 Numbers = 30 × 6
= 180

Sum of first 4 Number= 25 × 4
= 100

Sum of last 3 Numbers = 35 × 3
= 105

Hence
Fourth Number =
$= 100 + 105 - 180 \\ = 205 - 180 \\ = 25$
Therefore Fourth Number is 25


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Answer 2

Hi friends

Sum of 6 Number = 6 × 30 = 180

Sum of First 4 Number = 4 × 25 = 100

Sum of Last 4 Number = 3 × 35 = 105

Hence Fourth Number is

= 100 + 105 - 180

= 205 - 180

= 25

Hope it helps you

Thanks
@ MSD