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biology alevel serial dilution

hii
so i’m stuck in this question where the answer is 50, but i got 10.

i did 5% of 20, to get 0.1:9.9 to make up 10cm
so i thought the dilution factor was 100,

and then did the bacterial cells / by the dilution factor * 10 (cause 10 fold dilution?)

and then divided by 10 to go back from agar plate to last flask

i’m not sure why the answers 50
please help

thank you a bunch 🏔️

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A5AD9416-357F-46C5-A3FD-708446860EFB.jpg.jpeg

Reply 1

Student2011584

I think I do a different exam board as I don't do ten fold dilution series. But I've done what you did and got 50? 5% of 20 = 1, 5% of 10x10-6 = 50,000.
50,000/100 = 5000. 5000/10 = 500. 500/10 = 50?

I don't know if I've used the right dilution factor etc as I just used what you had but maybe you didn't correctly find the 5% of the bacteria ? Thats all I can think went wrong?

Sorry if I was no help!