1. Holiday Day
"What day do you go back to school, Harish?" asked his grandmother one day.
"Well," Harish replied, "Nine days ago, the day before yesterday was three weeks before the second day of term."
If Harish had this conversation on a Sunday, what day of the week did he start school?
From mathsisfun.com
Ans: Harish started school on Tuesday. The reasoning runs as follows: Today is Sunday. Nine days ago is 7+2 days ago. Seven days ago was Sunday too. That means that NINE days ago was Friday. On Friday, the day before yesterday was Wednesday. Three weeks later is Wednesday again. That is the second day of term. So the term began on Tuesday. Wasn't that easy?

2. Birds in Trees
There are 2 trees in a garden (called "White" and "Black") and in both trees are some birds. The birds of White tree say to the birds of Black tree that if one of you comes to our tree, then our population will be double yours.
Then the birds of Black tree tell the birds of White tree that if one of you comes here, then our population will be equal to yours.
How many birds are in each tree?
From mathsisfun.com
Ans: The solution is 7 birds on White tree, and 5 on Black tree. How do we see this? Let there be W birds on White tree and B birds on Black tree. So, if 1 bird comes from Black to White tree, their population will be double of Black's, that is, W+1=2(B-1). The factor (B-1) indicates that one bird has flown away from the Black tree. Re-writing this equation, 2B-W=3.
We need one more hint: if one bird from White comes to Black tree, then the populations will be equal: B+1=W-1. We can re-write this as W-B=2. Adding the two conditions, we have (2B-W)+(W-B)=3+2. Simplifying, B=5. This immediately gives W=7.