# Talk

## Q x Q x Q=1331. What is Q?

(11 Posts)
Erebus Fri 29-Jul-11 14:47:32

The Q's are the lengths of the sides of a cube. The volume of the
cube is 1131cm3

Fri 29-Jul-11 14:49:17

11

Fri 29-Jul-11 14:49:31

11

Fri 29-Jul-11 15:08:54

Do we win a prize?

moonferret Fri 29-Jul-11 15:11:14

Not for just pressing the cube root button on your calculators...lol

Fri 29-Jul-11 15:17:41

Ah, but I didn't (I couldn't find it )

Erebus Fri 29-Jul-11 15:24:25

No calculator allowed!

Seriously.

Y6 maths. I now recognise DS is supposed to try estimation to get there- recognising it's not 10 cubed, so trying 11.

Fri 29-Jul-11 15:32:01

DeWe Fri 29-Jul-11 17:52:18

If you're using estimation you can see immediately that 1331 > 1000
Cube root of 1000 = 10, Therefore cube root of 1331 >10

If you look at:
0^3 = 0
1^3 = 1
2^3 = 8
3^3 = 27
4^3 = 64
5^3 = 125
6^3 = 216
7^3 = 343
8^3 = 512
9^3 = 729

As only 1^3 ends in a 1, the answer must end in a 1 too.

As 20^ 3 =8000, The answer must be between 10 and 20 and end in a 1

Fri 29-Jul-11 20:22:10

I didn't understand any of that. It is just 11.

sproingle Sat 30-Jul-11 23:23:53

Agree. Doesn't need a calculator.

Clearly must be more than 10 as 10 cubed is 1000
Since 1 cubed is 1, worth trying 11.
11 x 11 = 121 and 121 x 11 = 1331 (neither of which are difficult calculations)

I don't think you need notice, as DeWe does that it must end in 1. That requires you to work out all those other cubes.

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