40% = 0.4
Explication:
40 / 100 = 0.4
Here is a photo of how I got the answers and what the answers are (Key: Red represents how I got the answers, while the highlighter shows what the answers are):
X + y = 21
x - y = 3
Adding the above equations, we get,
2x = 24
x = 12.
y = 21 - x
y = 21 - 12
y = 9.
Therefore,
No. of Pens = x = 12,
No. of Pencils = y = 9.
I think it is true. I hope this helps