What is the least number of buns that must be sold to make a profit of more than 5 pounds if 12 pounds is spent in making buns and each bun is sold for 80p?

Answer 1

Work in either pence or pounds.

£1 = 100p

→ £12 = 10 × 100p = 1200p

To make a profit, the money received must be more than the cost of the buns:

80p × number_of_buns > 1200p

However, as a profit of at least £5 is wanted, this must be added to the cost price to give the amount revenue must exceed:

1200p + £5 = 1200p + 500p = 1700p

This then gives:

80p × number_of_buns > 1700p

→ number_of_buns > 1700p ÷ 80p

→ number_of_buns > 21¼

As only whole buns are being sold, round up to the next whole number and at least that number must be sold:

number_of_buns ≥ 22

→ at least 22 buns need to be sold at 80p to make a profit of at least £5 when it cost £12 to make the buns.

Answer 2

0.8*B > 12 + 50.8*B > 17

B > 17/0.8 = 21.25

So B >= 22.