The Average marks of 13 student is 57. the average marks of 7 student is 61 and that of last 7 is 62 then find the marks of 7^th student?

Formula of Average :

Average = (a + b)y - nx

By Simple Method:

average of 13 student is= 57

average of first 7 student is= 61

average of last 7 student is= 62

1 2 3 4 5 6 7 8 9 10 11 12 13

(7 * 61 + 7 * 62) - 13 * 57

7 (61 + 62) - 13 * 57

7 (123) - 741

861 - 741

120

By Fats Trick:

For fast trick we put the values in the formula (a + b)y - nx

(61 + 62) 7 - 13 * 57

(123) 7 - 741

861 - 741

120

so the marks of 7^th student is 120.

Watch Youtube video of Speed and Time for better understanding.