Question

A pencil and two biros cost 1.80 . Two pencils and a biro cost 1.20.
What is the cost of 2 pencil?

Answer 1

Let the cost of a pencil be \( p \) and the cost of a biro be \( b \). We can create the following equations based on the information given:

1. \( p + 2b = 1.80 \) (Equation 1)
2. \( 2p + b = 1.20 \) (Equation 2)

To solve for \( p \) and \( b \), we can first rearrange Equation 1 to express \( b \) in terms of \( p \):

\[
2b = 1.80 - p
\]
\[
b = \frac{1.80 - p}{2}
\]

Now, we can substitute this expression for \( b \) into Equation 2:

\[
2p + \frac{1.80 - p}{2} = 1.20
\]

To eliminate the fraction, multiply the entire equation by 2:

\[
4p + (1.80 - p) = 2.40
\]

Now, simplify and combine like terms:

\[
4p - p + 1.80 = 2.40
\]
\[
3p + 1.80 = 2.40
\]

Subtract 1.80 from both sides:

\[
3p = 0.60
\]

Now, divide by 3:

\[
p = 0.20
\]

Now that we have the cost of a pencil, we can find the cost of 2 pencils:

\[
2p = 2 \times 0.20 = 0.40
\]

Therefore, the cost of 2 pencils is \( \boxed{0.40} \).