# order of operations: 3____4(21___7)___24 = 3.5

#### zcar46

##### New member
Hi I am a newbie trying to help my 7th son with homework. here is problem.

Fill in the blanks with the correct opertation symbols (+ - X /)
3____4(21___7)___24 = 3.5

I have been using trial and error. Is there another way to figure this out.
Thank you

#### Subhotosh Khan

##### Super Moderator
Staff member
Re: order of operations

zcar46 said:
Hi I am a newbie trying to help my 7th son with homework.
here is problem.
Fill in the blanks with the correct opertation symbols (+ - X /)
3____4(21___7)___24 = 3.5

I have been using trial and error. Is there another way to figure this out.

Nope - trial and error is it - may be sometimes educated guess - but ultimately trial and error.

Thank you

#### chivox

##### Junior Member
Re: order of operations

zcar46 said:
Hi I am a newbie trying to help my 7th son with homework.
here is problem.
Fill in the blanks with the correct opertation symbols (+ - X /)
3____4(21___7)___24 = 3.5

I have been using trial and error. Is there another way to figure this out.
Thank you
If you have a decimal in the final answer (3.5), there is probably a division involved somewhere, because logically, addition, subtraction, and multiplication with integers will not get you anything but an integer.

Try looking for a division by 24 as the last step. But it might be wrong. So if that doesn't work, trial and error is the way.

Also, since there are parentheses involved, those are only required (really) for addition and subtraction. You can probably rule out multiplication or division between the 21 and the 7.

Happy hunting....

#### Denis

##### Senior Member
Re: order of operations

zcar46 said:
3____4(21___7)___24 = 3.5
Are you sure EACH of the 6 numbers are correct? I think there's a typo in at least one of them.

#### chivox

##### Junior Member
Re: order of operations

Denis said:
zcar46 said:
3____4(21___7)___24 = 3.5
Are you sure EACH of the 6 numbers are correct? I think there's a typo in at least one of them.
+, /, / works with these numbers.

3 + 4 (21 / 7) / 24
3 + 4 (3) / (24)
3 + 12 / 24
3 + 0.5
3.5

The parentheses were a bit of misdirection for my adult brain. Don't worry: I'll get over it.

This type of exercise kind of feels like solving a sudoku puzzle. There are only so many possibilities for each square, so if you exhaust every one of them, one of them should work. I guess it's a good way to get kids to practice doing order of operations, but imagine how frustrating it can be.

#### mmm4444bot

##### Super Moderator
Staff member
chivox said:
... it's a good way to get kids to practice doing order of operations, but imagine how frustrating it can be.

You mean getting kids to practice is frustrating? :wink: