scrutinizer wrote:Obviously 21*4=84,so the next test is 5*21=?. That works, so that's your answer. If not, you'd look at the factors of 21. This method works for find the GCF of any two numbers.

Your method seems like you had to know 21 going in. It never would've occurred to me to start that far up the numbers. I was going "Well, both of them are divisible by 3… what about fou—oh crap, someone's rung in, too late."

Cut it any way you want math is something you just see.

Unless you're me.

Sherm wrote:I was going with seven and the minute it was negged, I saw 21. The equation question is really easy, it is 3X = 54, but you have to see it,

Which I didn't. I was like "Oh crap oh crap oh crap, where do I start?! That's way too much work for five seconds!!"

Sherm wrote:and know that 3 times 18 is 54, and I mean know it without have to really think about it. If you have to go 3 times 8 is 24, carry the two and 3 times one is three, plus two is five, so it is 54. You aren't getting a math question on jeopardy.

That's my problem I think. I'm just too slow mathematically for these questions, so I either just flail at them blindly or don't even try.

TenPoundHammer wrote:
That's my problem I think. I'm just too slow mathematically for these questions, so I either just flail at them blindly or don't even try.

Then just pause the screen and work it out. You don't start playing Liszt's Hungarian #2 at 110 beats per minute out of the gate; learn it slow then increase the tempo.

scrutinizer wrote:Obviously 21*4=84,so the next test is 5*21=?. That works, so that's your answer. If not, you'd look at the factors of 21. This method works for find the GCF of any two numbers.

Your method seems like you had to know 21 going in. It never would've occurred to me to start that far up the numbers. I was going "Well, both of them are divisible by 3… what about fou—oh crap, someone's rung in, too late."

The way "to know 21 going in" was mentioned in the post scrutinizer quoted: 105-84=21. And if you're looking for the highest common factor, you might want to start high. So start with the highest possibility, 21 (can't be bigger than higher number minus lower number), and if that doesn't fit, go to the factors of 21, as scrutinizer said. So 7 and 3 are the next two possibilities.