**Fast trick to find Average**

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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**

^{th}

### By Simple Method:

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average of 13 student is= 57

average of first 7 student is= 61

average of last 7 student is= 62

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13

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

7 (61 + 62) - 13 * 57

7 (123) - 741

861 - 741

120

### By Fats Trick:

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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**.

^{th}

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