s1!

...

The class width is the difference between the class boundaries.

So, what are the class boundaries for the 10-15 interval? They're not 10 and 15.
If you're not sure, reread the first sentence of your post.

S1

3. The variable x was measured to the nearest whole number. Forty observations are given in
the table below.
x 10 – 15 16 – 18 19 –
Frequency 15 9 16
A histogram was drawn and the bar representing the 10 – 15 class has a width of 2 cm and a height of 5 cm. For the 16 – 18 class find
(a) the width,

I'm really stuck even though this question is only worth one mark!

frequency = fdx class width
15=fdx5
fd=3

if a class width of 5 has a width on the histogram of 2

5k=2
k=0.4

so a class width of 2 should be
2x0.4= 0.8

but the answer is 1cm! and it's only worth one mark so i must be missing something incredibly obvious but i can't see what!