Friday

August 22, 2014

August 22, 2014

Posted by **sh** on Thursday, February 19, 2009 at 8:17pm.

ac+bd=38

ad+bc=43

what is a+b+c+d=?

multiple choice:

a)15 b)16 c)17 d)18 e)19

First, I tried guessing and testing, but couldn't find the correct answer.

Then I tried isolating a

a=(34-cd)/b

I'm stuck, there are too many variables

- math -
**drwls**, Thursday, February 19, 2009 at 9:07pmIn general, you are correct. There are not enough equations to solve for four variable. However they may be looking only for answers a,b,c,d that are integers. That restricts your options. Note that:

ab + cd + ac + bd = (a+d)(b+c) = 72

ab + ad + cd + bc = (a+c)(b+d) = 77

ac + bd + ad + bc = (a+b)(c+d) = 81

IF the solutions must be single-digit integers, the last equation tells you that

a + b = 9 and

c + d = 9

Therefore

a + b + c + d = 18

To solve for all four, you could say that

a + c = 11

b + d = 7

Which is consistent with a+b+c+d = 18

I can't find a way of satisfying

(a+d)(b+c) = 72

such that the sum of the two factors is 18.

I give up.

- math -
**sh**, Friday, February 20, 2009 at 1:11amWow, I never thought of combining it, thanks! The problem doesn't ask to solve for a b c & d

**Related Questions**

math - Beth Dahlke is taking a ten question multiple choice test for which each ...

math - Beth Dahlke is taking a ten question multiple choice test for which each ...

Math - a 10 question multiple choice test has 4 possible answer for each ...

math - What is the probability of guessing 70 out of 100 multiple choice ...

Stats - An instructor gives a test with 20 multiple choice questions. There are ...

apchemistry - I tried to figure this out with my standard reduction potentials ...

psychology statistics for behavioral sciences - A multiple-choice test has 48 ...

math - A multiple-choice test has 10 questions. Each question has 5 choices. If ...

statistic - A multiple-choice test has 48 questions, each with four response ...

Math - i tried and tried and i cant find the answer. is it not a solution. (3/x...