Question

The average of 15 numbers is 80. The first seven numbers and the last five numbers have averages of 90 and 54 respectively. The ninth number exceeds the eighth number by 20%, and the tenth number is reduced by (50/9)% from the ninth number. Determine the value of the ninth number.

Q: Answer-The average of 15 numbers is 80. The first seven numbers and the last five numbers have averages of...

Let eighth number is 10x So, ninth number 1.20 10x 12x Tenth number 8509 1100 12x 34x3 So, 10x 12x 34x3 80 15 7 90 5 54 1200 630 270 300 Or, 100x3 300 Or, x 9 So, ninth number 12 9 108

A 84

B 96

C 108

D 120

E 132

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The average of 15 numbers is 80. The first seven numbers and the last five numbers have averages of 90 and 54 respectively. The ninth number exceeds the eighth number by 20%, and the tenth number is reduced by (50/9)% from the ninth number. Determine the value of the ninth number.

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