Question

the average of 10 number is 65 if the average of first 9 number 64 find the tenth number​

Answer 1

Step-by-step explanation:

S10=65 ----------------------(i)

n { 2a+(n-1)d}=65

2

10 {2a+9d}=65

2

2a+9d=65×2

10

2a+9d=13------------------(ii)

S9=64--------------(iii)

9{2a+8d}=64

2

2a+8d=64×2

9

2a+8d=128 --------------------(iv)

9

Solve(ii)and(iv) equation

2a+9d=13---------(ii)

2a+8d=128---------(iv)

9

- -

d =11

9

___________

put d in (ii) equation

2a+9d=13

2a+9(11)=13

9

2a+11=13

2a=13-11

2a=2

a=1

Value of a=1 and d=11

9

Find a10

a10=a+9d

a10=1+9(11)

9

a10=1+11

a10=12

Tenth no. =12