Mind Benders

1. A cable, 16 metres in length hangs between two pillars that are both 15 metres high. The
ends of the cable are attached to the top of the pillars. At its lowest point, the cable hangs 7
metres above the ground. How far are the two pillars apart?

2. Kotak is a strange liar. He lies on six days of the week, but on the seventh day he always tells
the truth. He made the following statements on three successive days:
Day 1: “I lie on Monday and Tuesday.”
Day 2: “Today, it’s Thursday, Saturday or Sunday.”
Day 3: “I lie on Wednesday and Friday.”
On which day does Kotak tell the truth?

3. Below is an equation that isn’t correct yet. By adding a number of plus signs and minus signs
between the digits on the left hand side, the equation can be made correct.
123456789 = 100
How many different ways are there to make the equation correct?

Answers

1. The distance between the poles is 0 (zero).

2. Tuesday.

3. 11 different ways:
123+45-67+8-9=100, 123+4-5+67-89=100, 123-45-67+89=100, 123-4-5-6-7+8-9=100
12+3+4+5-6-7+89=100, 12+3-4+5+67+8+9=100, 12-3-4+5-6+7+89=100,
1+23-4+56+7+8+9=100, 1+23-4+5+6+78-9=100
1+2+34-5+67-8+9=100, 1+2+3-4+5+6+78+9=100