Question : The average of 8 numbers is 44. The average of the first three numbers is 50 and the average of the next two numbers is 52. If the sixth number is 6 and 8 less than the seventh and eighth numbers respectively, then what is the value of the eighth number?
Option 1: 36
Option 2: 32
Option 3: 40
Option 4: 56
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Correct Answer: 36
Solution : We know that, Average = $\frac{\text{Sum of all the observations}}{{\text{Total number of observations}}}$ Let the eight numbers as $a$, $b$, $c$, $d$, $e$, $f$, $g$, and $h$ respectively. From the problem, The average of 8 numbers is 44. $⇒\frac{a+b+c+d+e+f+g+h}{8} = 44$ ____(1) The average of the first three numbers is 50. $⇒\frac{a+b+c}{3} = 50$ ____(2) The average of the next two numbers is 52. $⇒\frac{d+e}{2} = 52$ ____(3) The sixth number is 6 less than the seventh number. $⇒f = g - 6$ ____(4) The sixth number is 8 less than the eighth number. $⇒f = h - 8$ ____(6) From equation 2, $⇒a+b+c = 150$ From equation (3), $d+e = 104$ Substituting $a+b+c$ and $d+e$ into equation (1), $⇒f+g+h = 44 \times8 - 150 - 104 = 98$ From equations (4) and (5), $⇒g = f + 6$ and $h = f + 8$ Substituting $g$ and $h$ into the equation $f+g+h = 98$, $⇒3f + 14 = 98⇒f = \frac{98 - 14}{3} = 28$ Substituting $f = 28$ into the equation $h = f + 8$, $⇒h = 28 + 8 = 36$ Hence, the correct answer is 36.
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