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How to calculate paint cost for two coats of a wall

Round the amount to buy upward

Compute $area \times coats \div coverage per litre$ , then round upward if paint is sold only in full litres. Rounding to the nearest litre could leave too little paint.

Problem

A wall is $6.5$ m long and $3$ m high and needs two coats. One litre of paint covers $10 m^{2}$ and costs 12 dollars. Paint is sold only by the full litre. What will the paint cost?

Answer

48 dollars for

4

litres.

The exact requirement is 3.9 litres; buying 3 litres would not cover both coats.

Step-by-step solution

1. Find the total area to coat

The wall area is $6.5 \cdot 3 = 19.5 m^{2}$ . Two coats require covering $2 \cdot 19.5 = 39 m^{2}$ .

2. Find the amount of paint

At $10 m^{2}$ per litre, $39/10 = 3.9$ litres are needed. Since only full litres can be purchased, buy $4$ litres.

3. Calculate the price

Four litres at 12 dollars per litre cost $4 \cdot 12 = 48$ dollars.

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