How_To_Be_Good_At_Math

CALCULATING • USING A CALCULATOR 157

Calculator questions

Now that you know all of the important

keys on the calculator and how to use them,

see if you can work out the answers to these

questions using a calculator.

983 + 528 =?

7.61 − 4.92 =?

−53 + 21 =?

39 × 64 =?

697 ÷ 41 =?

40% of 600 =?

TRY IT OUT

Equals key

This key is the “equals” key. When we

have entered a calculation on the keypad,

for example 14 × 27, we press [=] to reveal

the answer on the calculator’s display.

Memory keys

Sometimes it can be useful to get a

calculator to remember an answer, so that we

can come back to it later. [M+] adds a number

to the calculator’s memory and [M−] removes

that number. [MR] uses the number that is

stored in the memory, without us needing

to key it in and [MC] clears the memory.

Square root key

This key tells us the square root

of a number. We use this in more

advanced mathematics.

Percentage key

The [%] key can be used to work

out percentages. It works a little

differently on some calculators

compared with others.

Answers on page 319

Estimating answers

When you use a calculator, it’s easy to make

mistakes by pressing the wrong keys. One way

you can make sure your answer is right is to

estimate what the answer should be. We looked

at estimating on pages 24-25.

Let’s estimate the answer to 307 × 49

It’s quite tricky to work out in our heads so we

can round the numbers up or down. Round

307 down to 300, and round 49 up to 50.

300 × 50 gives the answer 15 000, so the

answer to 307 × 49 will be close to 15 000.

If we used the calculator to find 307 × 49

and got the answer 1813, then we would

know it's incorrect and that we missed a number

when keying it in. This is because estimating told

us that the answer should be close to 15 000.

307 × 49 =?

300 × 50 =?

300 × 50 = 15 000

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