
When a girl is 10, her sister is 4. When the girl is 60, what will her sister age?
Answer: 54
Solution:
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The combined age of Jack and John is 49. Jack is twice as old, as John was when Jack was as old as John is now. How old are the brothers?
Answer: Jack is 28 and John is 21.
Solution:

How do you calculate 1+2+3+4+5+6+7+8+9+10 quickly?
Answer: 55
Solution:
Answer : 55
The series “1+2+3+4+5+6+7+8+9+10” can be considered as the sum of the first 10 Natural numbers.
The generalized formula to find the sum of first N natural numbers is
(N * (N + 1) ) /2
For the series given, the value of N is 10
So substituting value of N in the generalized formula
( 10 * (10 + 1) ) / 2
= (10 * 11 ) / 2
= 110/2
Correct answer = 55
Answer : 55
The series “1+2+3+4+5+6+7+8+9+10” can be considered as the sum of the first 10 Natural numbers.
The generalized formula to find the sum of first N natural numbers is
(N * (N + 1) ) /2
For the series given, the value of N is 10
So substituting value of N in the generalized formula
( 10 * (10 + 1) ) / 2
= (10 * 11 ) / 2
= 110/2
Correct answer = 55