The table shows the currency exchange rate between Singapore dollars ($) and Thai Baht (THB) at a money changer. Before Adam went on a trip to Thailand, he went to the money changer. He changed $883 into Thai Baht at the money changer. Calculate how much Thai Baht he received. When Adam returned to Singapore, he had 2000 THB left.
He went to the money changer to change 2000 THB to Singapore dollars. Calculate how much he received. The price of a watch at the end of 2019 was 2% lower than at the end of 2018.
The price of the watch at the end of 2020 was 5% higher than at the end of 2019. Calculate the price of the watch at the end of 2020 as a percentage of the price at the end of 2018. Water demand in Singapore is currently about 430 million gallons a day with homes (domestic) consuming 45% and the non-domestic sector taking up the rest. Given that 250 litres is equal to 55 gallons, find the daily amount of water consumption in the domestic sector in litres.
Give your answer in standard form. Answer ___ litres. $1.08\times10^{-3}$ metres can be written as $k$ micrometres.
Find $k$. Answer $k=$ ___

1. Convert Singapore dollars to Thai Baht using the selling rate

The money changer sells $100$ THB for $4.415.

$\frac{883}{4.415}\times 100=20000$

So Adam received $20000$ THB.

1. Convert 2000 THB to Singapore dollars using the buying rate

Since the money changer is buying Thai Baht,
$2000\text{ THB}=\frac{2000}{100}\times \$4.088$
$=20\times \$4.088=\$81.76$

1. Represent the end of 2019 price as a percentage of the end of 2018 price

Let the price at the end of 2018 be $100\%$.

Since the end of 2019 price was $2\%$ lower,
$100\%-2\%=98\%.$

2. Apply the 5% increase from the end of 2019 to find the end of 2020 percentage relative to 2018

The end of 2020 price was $5\%$ higher than the end of 2019 price.

$98\%\times 1.05=102.9\%$

So the price at the end of 2020 was $102.9\%$ of the price at the end of 2018.

1. Find the domestic daily water consumption in gallons

Total water demand $=430$ million gallons.

Domestic consumption:
$45\% \times 430\,000\,000=0.45\times 430\,000\,000=193\,500\,000$
So domestic consumption is $193\,500\,000$ gallons.

2. Convert gallons to litres and express in standard form

Given $55$ gallons $=250$ litres,

$1\text{ gallon}=\frac{250}{55}\text{ litres}$

$193\,500\,000\times \frac{250}{55}=879\,545\,454.5\ldots$

In standard form,
$879\,545\,454.5\ldots = 8.79545\ldots \times 10^8 \approx 8.8\times 10^8$

1. Convert metres to micrometres

Since $1\text{ m}=10^6$ micrometres,
$1.08\times10^{-3}\text{ m}=1.08\times10^{-3}\times10^6=1.08\times10^3=1080\text{ micrometres}.$