17. The average of A and B is 20, a...
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17. The average of A and B is 20, average of B and C is 19 and average of C and A is 21. Find the value of A. (1) 22 (2) 20 (3) 18 (4) 24

11th - 12th Class
Maths
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17. (1) According to the question, [ begin{array}{l} A+B=20 times 2=40 B+C=19 times 2=38 C+A=21 times 2=42 end{array} ] Adding all the three equations, [ begin{aligned} 2(A+B+C) &=40+38+42 &=120 end{aligned} ] ( Rightarrow quad A+B+C=60 ) On subtracting Eq. (ii) from Eq. (iv), we get [ begin{aligned} A &=(A+B+C)=-(B+C) &=60-38=22 end{aligned} ]
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