Say they made 15 stereos
10 were basic
5 were deluxe
10x for basic
5(7/5)x = 7x for deluxe
7/(10+7) = 7/17
I solved correctly (A) using fractions ~ 3.5 min.
I have to say, picking numbers make a difference here, at least for me. (less than 2 min.)
how do you know to use the "picking numbers" method?
how do you choose the right numbers?
I'm weird in the sense that I never follow a set guideline or idea on how things should be solved. I look at a problem and just know how I'm going to attack it (it's not always the best way, but this strategy has worked well for me thus far).
In this case I saw that we were dealing with 2/3 of the stereos being basic and 1/3 being deluxe. Using this information alone I would choose a multiple of 3 (like 6, where 4 stereos would be basic and 2 would be deluxe).
However, I kept reading and saw that we were also dealing with time taking (7/5x) time to build them so I wanted to find a number that was a multiple of five to get rid of that fraction easily.
I just combined the two ideas and came up with 15 because it's the first number divisible by both 3 and 5.
Basically I just choose numbers that cancel out denominators wherever possible. Hope this helps!