Calculate six times eight minus
three minus two point six plus three point four.
Now to evaluate this expression,
we’ve got to think very carefully about the order of operations. And to help us to remember those,
we’ve got the acronym “PEMDAS”. P stands for parentheses. E stands for exponents. M and D stand for multiplication
and division and they both got equal precedence. And A and S stand for addition and subtraction and they’ve also got equal precedence. So the idea is we work our way down that list, picking out whether we’ve got parentheses, exponents, multiplication
and division, or addition and subtraction and do things in that order. So first of all, let’s look for
parentheses. And we do have some parentheses; so
we’re going to have to evaluate the contents of those parentheses first.
So first of all, let’s calculate
three take away two point six. Well the difference between three
and two point six is nought point four. We can see that on a number line
the jump from two point six up to three is nought point four. So we can replace three minus two
point six in parentheses with just a number nought point four. So now we’re left with the
expression six times eight minus nought point four plus three point four. So we’ve dealt with
parentheses. Are there any exponents or powers
or indices? No. So we’re looking for multiplication
and division. And we do have some multiplication,
six times eight. Now six times eight is forty-eight;
so we can replace that.
And there is no more multiplication
or division; so we’re just left with addition and subtraction. Now they’ve both got equal
precedence and we’d just work from left to right as we do them. So we’re gonna do forty-eight take
away nought point four first of all. So if we start off at forty-eight
and take away nought point four, we’re between forty-seven and forty-eight. And in fact we’re at forty-seven
point six, so we can replace these two terms here with forty-seven point six. And that leaves us with forty-seven
point six plus three point four.
Now that’s forty-seven point six
plus nought point four plus three or plus three plus nought point four; it doesn’t
matter which way around we do it. Well it just so happens if you look
at this forty-seven point six and nought point four, the nought point six and the
nought point four are gonna make a whole one. So I’m gonna go from forty-seven
point six plus nought point four will take me up to forty-eight. Now I need to add the three on as
well. So adding three on is gonna take me
up to fifty-one. So our answer is fifty-one.