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We can take the question in two ways. The average of two numbers increases by 20 when one of the numbers is doubled and increases by 25 when the other number is doubled. What must be the original average? or (The average of two numbers increases by 20 when one of the numbers is doubled) and (increases by 25 when the other number is doubled). What must be the original average?
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Let (x+y)/2 = z {"original average of two numbers"} ----- eqn-1
according to first condition (2x+y)/2 = z+20 ------- eqn-2
then according to second condition (x+2y)/2 = z+25 -----eqn-3
solve both eqn 2 & 3 and you will find x+y = (4z/3)+30
arrange the result as eqn-1 to find original average of two numbers
(x+y)/2 = (2z/3)+15 ----- eqn-4
compare eqn-1 & 4 i.e
z = (2z/3)+15
by solving it, the result will be 45.