Find missing Operation

Kodwo · **Posted:** Tue, 6 Dec 2011 05:04:41 UTC

If ∆ is an operation such that,
a ∆ b = ab + a – b, what does 4 ∆ 8 =?

How best can I approach this question?

Shadow · **Posted:** Tue, 6 Dec 2011 05:06:37 UTC

Kodwo wrote:

If ∆ is an operation such that,
a ∆ b = ab + a – b, what does 4 ∆ 8 =?

How best can I approach this question?

Just do the operation, a=4, b=8, so you need to calculate (4)(8)+4-8. . .

Kodwo · **Posted:** Tue, 6 Dec 2011 18:25:46 UTC

Shadow wrote:

Kodwo wrote:

If ∆ is an operation such that,
a ∆ b = ab + a – b, what does 4 ∆ 8 =?

How best can I approach this question?

Just do the operation, a=4, b=8, so you need to calculate (4)(8)+4-8. . .

4 ∆ 8 = (4)(8) + 4 - 8
4 ∆ 8 = 28
But I believe what the question is asking for is whether ∆ stands for plus,minus,division,multiplication?

Soroban · **Posted:** Tue, 6 Dec 2011 19:19:52 UTC

Hello, Kodwo!

Quote:

If ∆ is an operation such that: a ∆ b = ab + a – b,
what does 4 ∆ 8 = ?

The operation $\Delta$ has been defined.

$\text{Given }a\,\Delta\,b,\,\text{ it says: \:multiply }a\text{ and }b\text{ and add their ordered difference.}$

$\text{So . . . given }\:4\,\Delta\,8,\,\text{ we are to multiply }4\times 8\text{ and add }(4-8).$

$\text{So do it!}$

Soroban · **Posted:** Tue, 6 Dec 2011 20:01:13 UTC

Hello again, Kodwo!

Kodwo wrote:

But I believe what the question is asking for is whether ∆ stands for plus, minus, division, multiplication.

If so, the answer is: . $\Delta$ stands for a multiplcation, an addition and a subtraction.

No, it is asking for the value of $4\,\Delta\,8.$

Kodwo · **Posted:** Tue, 6 Dec 2011 20:26:47 UTC

Hi Soroban,

The answer is 28.I was looking for something else(what delta stood for.But I guess the question did not ask for that)

Shadow · **Posted:** Tue, 6 Dec 2011 23:34:30 UTC

Kodwo wrote:

Hi Soroban,

The answer is 28.I was looking for something else(what delta stood for.But I guess the question did not ask for that)

Indeed it doesn't, that's part of the point of it, it defines $\Delta$ , so it doesn't make much sense to ask for it after they just gave it to you.

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