10 tricky math riddles: can you crack them all?

1, 2, 3.

8-1, 16-1, 32-1, 64-1.
Each number in the sequence is multiplied by 2 to get the next. 1 is subtracted from each given number.

His sister is 99 years old. When Tom was 2 years old, his sister was 1 year old. 98 years later, he becomes 100 years old. And 98 years later, his sister will be 99 (98 + 1) years old.

The switch will be in the off position.
After switching 4 times, the switch will return to its original position.
3922 / 4 = 980 with remainder 2.
The switch will be at medium position after switching 3920 times, and at off position after another 2 switches.

He opens all 3 rings of 1 piece (3 operations). With these, he links the other 4 pieces together. This will give a total of 6 operations.

The case costs $5; the binoculars cost $95.

1 + 4 means 1 + 1(4) = 5
2 + 5 means 2 + 2(5) = 12
3 + 6 means 3 + 3(6) = 21
Then 8 + 11 means 8 + 8(11) = 96

5 minutes.

3² = 4 + 5

0.