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Calculation problem! Help!

  • 09-11-2010 5:44pm
    #1
    Tinker_Bella
    Closed Accounts Posts: 21 ✭


    I've an exam tomorrow and i was looking over calculation notes and came across a calculation question that I'm finding difficult to work out. Can you help?:confused:

    You are given 4ul of a 5ug/ul solution of human DNA in buffer. What volume of buffer should you add to the 4ul to give you a solution containing 2ug/ul?


    Any help wil be grateful!

    Thanks


Comments

  • #2
    GLaDOS
    Moderators, Regional East Moderators Posts: 23,233 Mod ✭✭✭✭GLaDOS


    5 ul/ug is a ratio of 5:1, and you need a ratio of 2:1. in your 4 ul you have 20 ug (4ul x 5 ug/ul). 20:4 is your 5:1 ratio. By adding 6 ul of buffer to your existing 4 you bring the ratio up to 20:10, i.e. 2:1

    Cake, and grief counseling, will be available at the conclusion of the test



  • #3
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    Is that right? - Is the answer not 10ul? The dilution factor to bring the solution from 5ug/ul to 2ug/ul is 2.5 (i.e. 5/2).

    Therefore, you must add 2.5x4ul=10ul to your 4ul solution to change it's concentration to 2ug/ul.

    Kevin


  • #4
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 93,274 Mod ✭✭✭✭Capt'n Midnight


    yes you want to end up with 10ul

    but you have to remember that you already have 4ul , so you only need to add another 6ul

    the devil as they say is in the detail


  • #5
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    haha... THAT part of this type of equation always 'got' me!

    Kevin


  • #6
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 93,274 Mod ✭✭✭✭Capt'n Midnight


    Kevster wrote: »
    haha... THAT part of this type of equation always 'got' me!

    Kevin
    My blind spot in physics was optics could never tell if it was a real or virtual image


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  • #7
    GLaDOS
    Moderators, Regional East Moderators Posts: 23,233 Mod ✭✭✭✭GLaDOS


    Thought I'd ****ed up for a second there :o

    Cake, and grief counseling, will be available at the conclusion of the test



  • #8
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    ...it was actually I who "****ed up" - haha


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