# Math Help - what number should be written in the brackets

1. ## what number should be written in the brackets

hello all , Can u please help me understand why c) 672 is thr right answear in this one :

156(108)138
260( ? )148

a)135 , b)448 , c)672 , d)158 , e )240

2. Are you sure that's how it's written? Are there no other information regarding that question?

3. hiya , yea thats exactly how its written and thats everything , supposed to find the logic in the numbers but i cant

4. Hello, edendeli!

If that's all that is given, there is no unique answer.

Help me understand why $(c)\;672$ is the right answer:

. . $\begin{array}{c}156(108)138 \\ 260(\;\;?\;\;)148 \end{array}$

. . $(a)\;135 \qquad (b)\;448 \qquad (c)\;672 \qquad (d)\;158 \qquad (e)\;240$

It doesn't help to say "That's exactly how it's written."
There must be some other clues somewhere . . .

Are those 9-digit numbers? . $\begin{array}{c}156108138 \\ 260abc148 \end{array}$

Are they sets of 3-digit numbers? . $\begin{array}{c}
156,\;(108),\;138 \\ 260,\;(abc),\;(148) \end{array}$

We can only guess at the intent of the problem.

Here's one guess . . .

Suppose the middle number is a function of the other two numbers.

. . That is: . $\begin{Bmatrix}f(156,138) &=& 108 \\ f(260,148) &=& ?\end{Bmatrix} \quad\Rightarrow\quad z\:=\:f(x,y)$

Then there are several brizillion possible functions.

Here's a function that produces answer $(c)\;672$

. . . . . $z \:=\:6(x-y)$

That is, subtract the two outer numbers, and multiply by 6.

But this function produces answer $(a)\;135$

. . $z \;=\;\dfrac{441}{2132}x + \dfrac{45}{82}y$

And this function produces answer $(e)\;240$

. . $z \;=\;\dfrac{714}{533}x - \dfrac{30}{41}y$

Conclusion: The author took too much cough syrup . . .

6. But thats exactly literally everything :
25 .What number should be written in the brackets below :
158(108)138
260( ? )148

... and the possible answears below that ...

" subtract the two outer numbers, and multiply by 6" - i think thats it

7. Hello, eveyone!

I still maintain that the problem is grotesquely silly . . .

Originally Posted by edendeli
"Subtract the two outer numbers, and multiply by 6"
i think thats it

That's only because we were given the answer.
. . By the way, how were you told that the answer is (c)?

To make my point, I made up a similar problem
. . without giving you the answer.

Given: . $f(1,2) \,=\,9$

Find: . $f(3,7)$

. . $(a)\;27 \qquad(b)\;28 \qquad (c)\;29 \qquad (d)\;30 \qquad (3)\;31$

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Spoiler:

$\text{If }f(x,y) \,=\,9x,\:\text{ then: }\:f(3,7) \:=\:9\!\cdot\!3 \:=\:27\;\text{ answer (a)}$

$\text{If }f(x,y) \:=\:7x+y,\:\text{ then: }\:f(3,7) \:=\:7\!\cdot\!3 +7 \:=\:28\;\text{ answer (b)}$

$\text{If }f(x,y) \:=\:5x+2y,\:\text{ then: }\:f(3,7) \:=\:5\!\cdot\!3 + 2\!\cdot\!7 \:=\: 29\;\text{ answer (c)}$

$\text{If }f(x,y) \:=\:3(x+y),\:\text{ then: }\:f(3,7) \:=\:3(3+7) \:=\:30\;\text{ answer (d)}$

$\text{If }f(x,y) \:=\:x+4y,\:\text{ then: }\:f(3,7) \:=\:3 + 4\!\cdot\!7 \:=\:31\;\text{ answer (e)}$

NOW do you believe me?

8. Hello again ,
I obviously havent made myself clear in my previous thread , first i meant thanks very much for taking your time replying to me , after that i just copied your suggested answear and just wrote that i think thats the right logic that they are looking for me to find ( the one you've given , not like i just found it myself ! ) and i yea i agree with you that is incredibly silly and makes no sense at all ,its from an expample test that includes 5 different moduls - maths , literature,history etc ,the maths one include 10 tasks with few " logical " problems , u only have a minute to asnwear each question as well , .... oh and i have the answeasr after each test so thats how i know its C the right answear !
and again thanks for your help .......