CPhill

.75=(x/230,000)    multiply both sides by 230,000

230,000 * .75  = x = 172,500

Here you go, Mackenzie......this website covers it in an easy-to-understand manner...

1.24 x 10^-3   =   .00124

And

9.1 x 10^-4  =  .00091

So, we just subtract like we normally would....

   .00124

-  .00091

  ----------

   .00033mm

And that's it !!!

This is a rather broad topic....do you have any specific questions??

Thanks, BJ...!!!

Thanks, GUH  !!!

Very nice, Melody.....maybe one day I'll catch on to probabiity.....but, it's not probable...!!!!

Melody, the poster seems to have asked one question in the "large print" and a different one in the "fine print"......LOL!!!

Yep..that looks correct.....I love these "Brain Teasers".....!!!

I'm just doing this one to see if I can solve it without "cheating" and looking at other's answers.....!!!

Let N be the total number of stamps....so we have

C + D   = 49/70N   (1)

B + D  = 60/70N    (2)

B + C = 620

Adding (1) and(2), we have

620 + 2D  = (109/70)N  → D = (109/140)N - 310

So

B + C + D  = N

620 + (109/140)N - 310  = N

310 = (31/140)N →   N = 1400

So D has  (109/140)(1400) - 310 = 780

And B has

780 +  = (6/7)(1400) → D = 1200 - 780 = 420

So D - B = 780 - 420 = 360 more