25

The grandfather is 64 years old,
John is 37 years old and Antony is 2 years old.

Z = grandfather
Y = John
X = Antony
Y + 24 = Z
X + 35 = Y
X + Y + Z = 100
Z = X + 59
=> X + X + 35 + X + 59 = 100
3X + 94 = 100 =>
3X = 6 => X = 2
Y = 37
Z = 61

There is a 50/50 chance of each toss being either heads or tails. The previous toss does not impact the next toss.

4 days
Day 1: 2 -1 = 1
Day 2: 1 +2 -1 = 2
Day 3: 2 + 2 - 1 = 3
Day 4: 3 +2 = 5.

888+88+8+8+8=1000

c) 24

With three cats would be enough.
Since if each cat managed to catch a mouse per minute between the three, in a hundred minutes they would hunt a hundred mice.

Four years ago.

Milly $620 Billy $220
Milly 620 – 60 = 560 Milly 620 + 10 = 630
Billy 220 + 60 = 280 Billy 220 – 10 = 210

1, 2 and 3
1 + 2 + 3 = 1 x 2 x 3 = 6

The original length of belt was 96 cm.

The oldest sister is 9 years old and the younger ones are both 2.