Mohamed, hello and thank you so much for your feedback! In looking over the slide and the tutorial video that goes with it, I initially thought I might have used 10^7 instead of the 10^8 for the OSPF Reference Bandwidth value - which would have been a terrible mistake on my part. However, in looking at the slide, the value listed is 10^8 written out in decimal (so, 100,000,000 - which is 100Mbps represented as bits per second). I do see, however, where that might have caused some confusion (and I am very sorry for that!) as I have '[interface speed]' instead of maybe adding in 'in bits per second (bps)' to make things more clear since that was the unit of measure I was working with in the example. During the video (which you have pictured below the initial slide) It looks like I am showing how changing the cost of the OSPF Reference Bandwidth value would result in a cost of 1 depending on the link speed and the value you use. So, when I increased The OSPF Reference Bandwidth to 1Gbps (and in the actual command you enter the value in Mbps, so the command under the OSPF global configuration section would be: 'auto-cost reference-bandwidth 1000' - and that could be a bit confusing as well when transitioning between units of measure as well) that results in a value of 1,000,000,000 in bits per second. For 10Gbps we just add in another '0' and the idea was to show the equivalent value for the interface/link speeds in bits per second. Again, my apologies for any confusion this might have caused you and I hope this provides some clarification and again, thank you so much for your feedback!
Author: The CCNA Candidate's Guide to OSPF