The average of group of 13 boys is 13. when two more boyss joined the group, the average age rose by 2 years .the sum of ages of two new boys

56 years

Step-by-step explanation:

we know that

1) The average of group of 13 boys is 13 years

so

Remember that

The average is the sum of the ages divided by the number of boys

The sum of the ages is equal to the average multiplied by the number of boys

The number of boys is 13

The average is 13

The sum of the ages is > 13*13=169

2) When two more boys joined the group, the average age rose by 2 years

so

Now the number of boys is 13+2=15

The average is 13+2=15

The sum of the ages is > 15*15=225

To find out the sum of ages of two new boys, subtract the original sum of the ages from the new sum of the ages

225-169=56 years

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step-by-step explanation:

1+2+3+4+5+6+7+8+9+10 = 55

2*10 = 20

55-20 = 35