Easy Puzzles 

Workings

Hint
How many students study chemistry and physics, but not biology?

Answer
500 students.

Reasoning
The answer is more easily seen if three intersecting circles are drawn, and the numbers inside each section are worked out.

We know that 73 students study all three disciplines, which allows us to work out the numbers.

97 students study chemistry and physics, so 97 − 73 = 24 study just chemistry and physics.
138 students study physics and biology, so 138 − 73 = 65 study just physics and biology.
152 students study chemistry and biology, so 152 − 73 = 79 study just chemistry and biology.

280 students study chemistry, so 280 − 73 − 24 − 79 = 104 study just chemistry.
254 students study physics, so 254 − 73 − 24 − 65 = 92 study just physics.
280 students study biology, 280 − 73 − 65 − 79 = 63 study just biology.

For a total of: 104 + 92 + 63 + 24 + 65 + 79 + 73 = 500 students.

Workings

Hint
How many 1 x 1 squares are there?

Answer
91 squares.

Reasoning
Squares of size:
   1 x 1 = 36
   2 x 2 = 25
   3 x 3 = 16
   4 x 4 = 9
   5 x 5 = 4
   6 x 6 = 1

Total = 36 + 25 + 16 + 9 + 4 + 1 = 91.

Workings

Hint
How many reservoirs can each drain in 36 hours?

Answer
7 hours and 12 minutes.

Reasoning
We can use a time that 12 hours and 18 hours both fit in to, in 36 hours:

   6 large pipes can drain 3 reservoirs.
   6 small pipes can drain 2 reservoirs.

Therefore, together, 6 large and 6 small pipes can drain 5 reservoirs.

36 hours ÷ 5 = 7.2 hours for one reservoir.

7.2 hours = 7 hours and 12 minutes for one reservoir.

Workings

Hint
Break the word down in this way: GH-O-TI.

Answer
Fish!

Reasoning
The GH as in ENOUGH = F.
The O as in WOMEN = I.
The TI as in MOTION = SH.