4. The world's largest coin, made by the Royal Mint of Canada, was auctioned in June 2010 The coin has mass $100 \mathrm{~kg}$, whereas a standard British $£ 1$ coin has mass $10 \mathrm{~g}$. What sum of money in $£ 1$ coins would weigh the same as the record-breaking coin?
A $£ 100$
B $£ 1000$
C $£ 10000$
D $£ 100000$
$\mathrm{E} £ 1000000$
Solution: $\mathbf{C}$
We have to work out how many $£ 1$ coins, each weighing $10 \mathrm{~g}$, we need to get a total weight of $100 \mathrm{~kg}$. Now $1 \mathrm{~kg}=1000 \mathrm{~g}$, and so $100 \mathrm{~kg}=100,000 \mathrm{~g}$. So we need $\frac{100,000}{10}=10,000$ of these coins. That is, $£ 10000$ in money.