Decimals

NZ Level 5

Solve problems involving both an addition and a subtraction

Lesson

Just like with whole numbers, we can solve decimal number problems by using some useful skills we already know, such as:

- adding decimals,
- subtracting decimals,
- following the order of operations, and
- the role of place value in decimals.

In Video 1, we're going to solve $16.83-13.81$16.83−13.81, by working across our page, and thinking about place value.

It's a really good idea to work out an estimate first, so that you can see if your answer is reasonable or not. This helps identifies things like numbers being in the wrong place column.

In Video 2, we're going to estimate, then solve $0.47+0.52-0.31+0.21$0.47+0.52−0.31+0.21. We'll need to think of the order of operations, since this problem has several parts. Then we will compare our final answer to our estimated answer.

Sometimes you might find that you are not able to add or subtract without regrouping. We look at how to solve those problems, using a vertical algorithm to help us, in Video 3. It might be useful to look at Regrouping with whole numbers before using the same process with decimals.

Remember!

There's often more than one way to solve number problems. Just remember that the order of operations *must* be followed.

Find $8.9-\left(1.5+3.3\right)$8.9−(1.5+3.3) giving your answer as a decimal.

Find $79.49-\left(76.91-14.14\right)$79.49−(76.91−14.14) giving your answer as a decimal.

Find $8.226+1.513-6.523$8.226+1.513−6.523 giving your answer as a decimal.

Understand operations on fractions, decimals, percentages, and integers