Question

The average of 3 numbers is 10. If the
average of first 2 numbers is 9, find the
third number,
(1) 12 (2) 13
(3) 14
(4) 15​

Answer 1

Answer:

12 is the third number

Step-by-step explanation:

let the first two number be x and y( x+y)=18

because (x+y)/2=9 so 2*9=18

the average of three number is 10 let the third number be z( x+y)is 18

3*10=30 the sum of the three number =30

x+y+z=30

18+z=30

z=30-18

z=12

Answer 2

Answer:

The average of first two no. is 9

average :- sum of all quantities \no. of quantities

total no. = 2

average =9

let the sum of no. be x

x\2=9

x=2×9

x=18

the sum of first two no. is 18

3rd no. :- (18+x)\3=10

18+x=10×3

18+x=30

x=30-18

x=12

so, the third no. is 12

answer :- (1)12