## How thick are their walls?

Are you able to estimate the thickness of the walls of these particular shipping containers, based solely on the information you see in the photo?

## Assuming…

• their walls are uniform thickness all over (which is doubtful!)
• they are made entirely of steel, with a density of 8000 Kg / m3

I think this is a fun little bit of photo-detection. Perfect to put on your resume for the CIA!

## Gross, Net & Tare Weights

Gross weight – Tare = Net weight

http://www.canscale.com/

Example: The gross weight of a tin of biscuits includes the tin and the biscuits. The Net weight is the weight of just the biscuits, and the tare in this case would be the weight of the tin. Simple!

## What is the germination rate of these saved lettuce seeds?

I planted 1 lettuce seed in each of these circular ‘cells’ 4 days ago.

Do you think they are growing well? Explain how you know.

Can you work out the fraction that have germinated?

Not all seeds will grow successfully. Sometimes seed packets show a germination percentage rate (%). In other words, this tells you on average how many seeds out of 100 you would expect to germinate.

A gardener sowed 100 of the Calendula ‘Fiesta Gitana’ seeds shown above. She observed that 90 of the seeds germinated successfully. Compare her results with the germination percentage shown on the seed packet.
Can you explain why they are different?

You can convert your germination fraction into a ‘germination
percentage rate’, like we saw on these seed packets like this:

1. Identify the numerator (top) and denominator (bottom) of your fraction.
2. Use a calculator to divide the numerator by the denominator.
3. This gives you the decimal equivalent to the fraction.
4. Multiply this by 100 to calculate the percentage. That’s it!

Write your result into your worksheet now.

Challenge! If you want to practise your numeracy skills, try to convert from the fraction to the percentage without using a calculator (or a safety rope!).

HINT: First try to find an equivalent fraction with a denominator that is a factor of 100.

## Definitions

• Numerator: the top number in a fraction
• Denominator: bottom number in a fraction
• average: a number that describes the middle value of a set of data
• percentage: a fraction expressed with a denominator of 100 written with this symbol %, which is actually the units in 100 rearranged!