Operations with Decimal Numbers

In a cell phone accessory store, Mateo wants to buy a case costing $249$ pesos and a screen protector costing $178$ pesos. If Mateo pays with a $1\,000$ pesos bill, how much change will he receive at the register?

Copy and complete the following statements by writing the missing decimal number to make each calculation correct:

1. a) $15.45 + \dots = 20$
2. b) $7.2 - \dots = 4.55$
3. c) $\dots \times 3 = 12.9$

Three friends decide to have an afternoon snack together. They buy a pack of soft drinks for $97$ pesos, a family-size bag of chips for $46$ pesos and a box of small cakes for $109$ pesos. If they pay with a $400$ pesos bill, how much money will they have left over to buy candy afterwards?

Work out these calculations mentally using powers of ten. Remember to move the decimal point to the correct side depending on whether you multiply or divide:

1. a) $34.57 \times 10$
2. b) $0.23 \times 100$
3. c) $458.2 : 10$
4. d) $12.5 : 1000$

An athlete is training on a circular track. Each lap of the track is $0.45$ km long. If today she completed a total of $12$ laps, how many kilometers did she cover in total? If her goal was to run $6.3$ km, how many more laps should she have completed?

A marathon runner has completed a stage of $15.6$ km in an hour and a half ($1.5$ hours).

1. a) What was their average speed in km/h?
2. b) If they maintain the same speed, how many kilometers will they cover in $2.25$ hours?

To make a recipe, we need to divide a $1.5$ kg bag of flour into $6$ equal portions to make muffins. How many kilograms of flour will each portion weigh? Express your answer in grams as well.

A spool of filament for a 3D printer weighs exactly $1.25$ kg. If $0.015$ kg of plastic is used to make a small part, how many complete parts can be made from a single spool? How much filament will be left over at the end?

We are cooking a recipe that requires $0.250 \text{ kg}$ of flour to make $6$ muffins. If we want to invite the whole class ($28$ students) and we want each of them to eat $2$ muffins:

1. a) How much flour will we need in total? Express the result in kilograms.
2. b) If we buy flour packets of $0.75 \text{ kg}$, how many packets will we need to buy at least? How much flour will we have left over exactly?

Work out the following combined operations, respecting the order of operations (brackets, multiplications/divisions, and finally additions/subtractions):

1. a) $4.5 + 2.1 \times 3$
2. b) $(12.8 - 3.4) : 2$
3. c) $5 \times 0.25 + 1.75$

A group of $4$ friends goes to the cinema. The total for tickets and popcorn came to $45.80$ pesos. If they decide to split the cost equally, how much money must each person pay? If one of them only has a $10$ pesos note and a $2$ pesos coin, will they have enough money?

Calculate the result of the following combined operations, respecting the order of operations:

1. a) $12.5 + 3.8 \times (6.4 - 2.15)$

1. b) $(15.4 + 8.6) : 2.5 - 1.02 \times 4$

A municipality wants to fence a rectangular park measuring $25.4$ meters long and $12.75$ meters wide. The price of the fence is $304$ pesos per meter. If the total available budget is $24\,000$ pesos, do they have enough money to enclose the entire park? Justify your answer with the necessary calculations.

Calculate the result of the following mixed operation, strictly respecting the order of operations and working with all decimal places obtained:

Once the final result is obtained, approximate it by rounding to the nearest hundredth and by truncating to the nearest tenth.