快猫短视频

#160 Blurry-Ness

Click! The camera shutter opened and closed just as the creature鈥檚 head ducked back beneath the surface of the lake, creating a large ripple.

鈥淚 got it! I finally got a picture of the Loch Ness monster!鈥� exclaimed Lily. She looked at the result on her digital camera. 鈥淚t鈥檚 blurry!鈥� She hung her head in defeat.

The boat passed directly over the spot where they saw the creature, but it was nowhere to be found. 鈥淗ow far away do you think it was when I took the picture?鈥� Lily asked Amelia later that day.

鈥淲ell, we were travelling in a straight line at 2 metres per second towards where we saw Nessie, and it took us 5 seconds to reach that large ripple it created, and another 10 seconds to get to the other side of the ripple. So that means it was 5 seconds plus an additional 5 to the middle of the ripple, which would make it 20 metres!鈥�

鈥淪adly, I think your maths is as fuzzy as my photo,鈥� said Lily.

How far away was the monster at the time the picture was taken?

Solution next week

#159 Express coffee

Solution

The location with the smallest combined distance is B.

Suppose the depot is lined up with the vendor that is fourth from the left (the 鈥渕iddle鈥� vendor). If the depot is moved to the left of this, the combined distance of the three vendors to the left will reduce, but the combined distance for the four on the right will increase by the same amount, so the overall combined left-right distance will increase.

Similarly, if you align the depot with the vendor that is fourth from the top, any change in the vertical coordinate will increase the total distance.

Kim has realised that the depot should be in the horizontal and vertical position of the middle vendors in those two directions, which is B.