Puzzle 25
A large freshwater reservoir has two types of drainage system. Small pipes and large pipes.
6 large pipes, on their own, can drain the reservoir in 12 hours.
6 small pipes, on their own, can drain the reservoir in 18 hours.
How long will 6 large pipes and 6 small pipes take to drain the reservoir?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
Share link – www.brainbashers.com/puzzle/znec
Hint
What would happen in 36 hours?
Answer
7 hours and 12 minutes.
Firstly we find a time that both 12 hours and 18 hours would 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.
7.2 hours = 7 hours and 12 minutes.
Puzzle 26
My current age is the age of my favourite book (which is 14 years old) plus one third of my age.
How old will I be when my favourite book is twice its current age?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
Share link – www.brainbashers.com/puzzle/znth
Hint
A little algebra might help.
Answer
I will be 35 in 14 years.
Reasoning
I am currently 21.
If X is my current age, then:
X = 14 + X
—
3
so
2X = 14
——
3
and
2X = 42
So
X = 21
I am currently 21 and my favourite book is currently 14 years old, when it is 28 years old (double its age) I will be 35.
Puzzle 27
Starting in the bottom left corner and moving either up or right adding up the numbers along the way, what is the largest sum you can make?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
Share link – www.brainbashers.com/puzzle/zqio
Hint
You can only go up or right.
Answer
28.
Puzzle 28
Yesterday I went for a short bicycle ride around the local lakes. As the weather was very hot, I rode in shorter stages than I'd normally ride.
In the first stage, I rode half of the overall distance.
Stage two saw half of the remaining distance plus 35 metres covered.
Stage three covered three-quarters of the remaining distance.
Stage four completed half of the remaining distance plus 75 metres.
Stage five completed the journey with a final burst of 150 metres.
How far did I cycle in total?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
Share link – www.brainbashers.com/puzzle/zofe
Hint
Try working backwards.
Answer
7,340 metres.
Reasoning
Stage 5's clue tells us that 150m was left. So the distance left at the start of Stage 4 must have been:
Dist4 = Dist4 + 75 + 150
—————
2
Which simplifies to give Dist4 = 450m.
Stage 3's clue tells us that 450m was one quarter of the remaining distance, so Dist3 = 1,800m.
Stage 2's clue tells us that the distance at the start of Stage 2 was:
Dist2 = Dist2 + 35 + 1800
—————
2
Which simplifies to give Dist2 = 3,670m.
Stage 1's clue tells us that 3,670m was half the overall distance, which means the entire ride was 7,340m.
Double-Checking
Starting with 7,340m:
Stage 1: cycled 3,670m, leaving 3,670m
Stage 2: cycled 1,870m, leaving 1,800m
Stage 3: cycled 1,350m, leaving 450m
Stage 4: cycled 300m, leaving 150m
Stage 5: cycled 150m, leaving 0m
< previous next >
