Question 304764
5 years ago,the average age of p and q was 15 years.
 average age of p,q and r today is 20 years.
 how old will r be after 10 years?
:
"5 years ago,the average age of p and q was 15 years."
{{{((p-5)+(q-5))/2}}} = 15
{{{(p+q-10)/2}}} = 15
multiply by 2
p + q - 10 = 30
p + q = 30 + 10
p + q = 40
:
"average age of p,q and r today is 20 years."
{{{(p+q+r)/3}}} = 20
Multiply by 3
p + q + r = 60
:
Subtract the 1st equation from the above equation
p + q + r = 60
p + q + 0 = 40
--------------------subtraction eliminates p & q
r = 20 age now
:
 how old will r be after 10 years? r = 30