Lesson video

Hi, I'm Miss Davies.

In this lesson we're going to be substituting positive terms into a formula.

We've been told that a is equal to five, and b is equal to seven.

Let's take up the value of 4a.

This means four multiplied by a.

Given that a is five, we can substitute this into our equation to say that four multiplied by five is equivalent to 4a.

Four multiplied by five is 20.

Next we've got 7a subtract three.

Substituting five into this expression, we can say seven multiplied by five subtract three.

This is equivalent to 35 subtract three, which gives us an answer of 32.

Our final example is a squared subtract b.

A squared is five squared, b is seven.

So by substituting these values in, we've got five squared subtract seven.

This is equivalent to 25 subtract seven which gives an answer of 18.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

Make sure that you are following the order of operations once you've substituted.

Calculate the brackets first then work with any powers followed by multiplication and division, and finally addition and subtraction.

We have been given the formula t equals 3k.

We're asked to work out the value of t when k is equal to four.

We know that 3k means three multiplied by k, so we can substitute the value four into the formula in the place of k to give t equals three multiplied by four.

This means that when k is equal to four, t is equal to 12.

With this question, we've been asked to find the value of k when t is equal to 51.

You can substitute this into our formula to be 51 is equal to three multiplied by k.

We're going to solve this by using inverse operations.

The inverse of multiplying by three is dividing by three.

To find k we need to divide both sides by three.

This means k is found by dividing 51 by three.

This gives an answer of 17.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

In part a, you're needed to do the calculation 10 multiplied by 16 subtract five.

This gives an answer t is equal to 155.

In part b, after substituting in the values, you have the equation 20 equals 10r subtract five.

To solve this equation, we're needed to add five to both sides and then divide by 10.

This gives an answer of r equals 2.

5.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

In part a, after making the substitutions, you both have the calculation 0.

5 multiplied by six add eight, multiplied by five.

This gives an answer of x equals 35.

In part b, after substituting, you will form the equation 30 equals 0.

5 multiplied by 10 add 20 multiplied by h.

To solve this equation, you're needed to start up by dividing by 0.

5.

This is the same as multiplying by two.

This gives the equation 60 equals 30h as 10 add 20 is 30.

This means that h is equal to two.

That's all for this lesson, thanks for watching.