Maths Degree Just For Shopping

I was shopping at the local supermarket and comparing the prices of things, as you do.

The pricing structure for the fruits button had me stumped

The first pricing £0.45p per 18g  packet

15.7p per 100g

Any 5 for £2.00

therefore 1 packet is £0.40 per 18g packet

Second pricing £0.45 per 18g packet

£2.50 per 100g

Any 5 for £2.00

therefore 1 packet is £0.40 per 18g packet.

Third pricing was for a Box of 5 packets at £2.19

 60.9p per 100g

therefore 1 packet is £0.43 per 18g packet

Any 2 Box of 5 in a pack for £3.50

therefore 1 packet £0.35p

 

So from that we can established that they are 4 different prices to consider

Buy only one packet pay £0.45 per 18g packet

Buy 5 individual packets pay £2.00 at £0.40 per 18g packet

Buy a Box 5 packets inside pay £2.19 at £0.43 per 18g packet

 Buy 2 boxes 10 packets in total pay £3.50 at £0.35 per 18g packet

From that we can deduce the price per 100g since the shop is using that at as a price comparison.

£0.45 per 18g therefore 100g cost £2.50

£0.40 per 18g therefore 100g cost £2.222

£0.438 per 18g therefore 100g cost £2.43

£0.35 per 18g therefore 100g cost £1.944

Ok so we have come to the conclusion of all the prices per 18g pack and price per 100g.

 so where does the  15.7p per 100g from the first pricing and 

60.9p per 100g from the 3rd pricing comes from!!!!

Why couldn't the shop just say that is the cost per packet at 18g rather than 100g

When I was looking at it in the shop it took me a few minutes to decipher the pricing structure.

Making sure I was comparing like for like. 

Why is the 2 box of 10 packets £0.10 cheaper which meant that 

Sam only got 2 flavours rather then the 3 different types of flavours

I had to go home and sit and work it all out with a calculator to get the 100g price comparison.

I don't have time to do that when I am shopping!!!

Its my little bug bear. grrrr