What is the sum of the ages?

Algebra Level 2

A man went to a house where some women were there. The man asked for there ages but they declined to give their individual age, instead they said - "We do not mind giving you the sum of the ages of any two ladies you may choose". Thereupon the man said - "In that case please give me the sum of the ages of every possible pair of you". They gave the sum as follows: 30 , 33 , 41 , 58 , 66 , 69 30,33,41,58,66,69 . The man took this figures and happily went away. What is the total sum of the ages of the women?


This is from the set Problems for everyone!!!


The answer is 99.

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1 solution

S P
May 30, 2018

Let there be n n number of women [where n N \color{#D61F06}{n\in\mathbb{N}} ]. It is given that the Total combination = 6 \text{Total combination} =6

( n 2 ) = 6 n ! 2 ! ( n 2 ) ! = 6 n ( n 1 ) 2 = 6 n 2 n 12 = 0 n 2 4 n + 3 n 12 = 0 n ( n 4 ) + 3 ( n 4 ) = 0 ( n 4 ) ( n + 3 ) = 0 Thus, n = 4 or 3 Since, n N : n = 4 \therefore \begin{aligned}& \binom{n}{2}=6 \\& \implies \dfrac{n!}{2!(n-2)!}=6\\& \implies \dfrac{n(n-1)}{2}=6\\& \implies n^2-n-12=0\\& n^2-4n+3n-12=0\\& n(n-4)+3(n-4)=0\\& \implies (n-4)(n+3)=0\\&\\& \color{#3D99F6}{\text{Thus,} ~n=4~\text{or}~-3}\\&\\& \text{Since,}~\color{#D61F06}{n\in\mathbb{N}}:~ \color{#20A900}{n=4}\end{aligned}

Thus there are 4 \color{#20A900}{4} number of women.

Let thier ages be a , b , c , d a,b,c,d

If a < b < c < d { a + b = 30 (1) a + c = 33 (2) a + d = 41 (3) b + c = 58 (4) b + d = 66 (5) c + d = 69 (6) \therefore \text{If} ~a<b<c<d~\begin{cases}& a+b=30 ~~-~~\text{(1)}\\& a+c=33 ~~-~~\text{(2)} \\& a+d=41~~-~~\text{(3)}\\& b+c=58~~-~~\text{(4)}\\& b+d=66~~-~~\text{(5)}\\& c+d=69~~-~~\text{(6)}\end{cases}

Hence, by (1) + (2) + (3) + (4) + (5) + (6) \text{(1)}+\text{(2)}+\text{(3)}+\text{(4)}+\text{(5)}+\text{(6)} we have:

3 ( a + b + c + d ) = 297 a + b + c + d = 99 \begin{aligned}&3(a+b+c+d)=297\\& \implies a+b+c+d=\boxed{99}\end{aligned}

The oldest 2 women's age sum=69,and the youngest 2 women's age sum=30,so it's 69+30=99

X X - 3 years ago

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