Grandfather's Present Age

Algebra Level 2

The average age of five members of a family is 21 years. If the age of grandfather be included, the average is increased by 9 years. The age of the grandfather is:


The answer is 75.

John Aries Sarza by John Aries Sarza , 26, Philippines

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3 solutions

John Aries Sarza
Aug 27, 2014

Let 21 ( 5 ) + x 21(5)+x be the summation of all members of the family including the grandfather 21 ( 5 ) + x 6 = 30 \frac { 21(5)+x }{ 6 } =30 x = 75 \boxed{x=75}

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The total age of the five family members is 5 ( 21 ) = 105 5(21)=105 . Therefore

105 + x 6 = 21 + 9 \dfrac{105+x}{6}=21+9

105 + x 6 = 30 \dfrac{105+x}{6}=30

105 + x = 180 105+x=180

x = 75 \color{#D61F06}\boxed{x=75}

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Ramiel To-ong
May 29, 2015

Sum of the five members = 21x5 = 105 105+G/(5+1 ) = 21 + 9 G = 75 age of grandpa

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