Grades 1-2 Video Solutions 2019-2019Levels12prob19

Video Transcription

Problem number 19. There are 10 camels in a zoo. The camels are either Bactrian, with two humps, or Dromedary, with one hump. In total, there are 14 humps.  Find the number of Bactrian camels in the zoo. A, 1, B, 2, C, 3, D, 4, E, 5.  If all 10 camels were Dromedary camels, there would be only 10 humps. Each Bactrian camel will have one more hump than a Dromedary camel. If 10 Dromedary camels had 10 humps,  switching out one of the Dromedary camels into a Bactrian camel will give us one more hump, or 11 humps. We can keep doing this until we get 14 humps.  If we have one Bactrian camel and the rest are Dromedary, there are 11 humps. If we have two Bactrian camels, there are 12 humps. Three Bactrian camels gives us 13 humps,  and four Bactrian camels gives us 14 humps, which is what we're looking for. So, if out of the 10 camels, four are Bactrian and the remaining six are Dromedary,  there will be 14 humps. Let's check this again. The four Bactrian camels give us four times two, which is eight humps, and the six Dromedary camels will give us six humps.  Eight plus six is 14, so there are four Bactrian camels in the zoo. The answer is D.

Video Summary

There are 10 camels in a zoo, either Bactrian (two humps) or Dromedary (one hump), totaling 14 humps. Assuming all camels are initially Dromedary with 10 humps, converting a Dromedary camel to a Bactrian adds a hump. By converting successively, four conversions of Dromedary to Bactrian achieve 14 humps. Thus, 4 Bactrian camels with two humps each and 6 Dromedary camels achieve the total: 4 Bactrian camels contribute 8 humps, and 6 Dromedary camels contribute 6 humps, totaling 14. Therefore, there are 4 Bactrian camels, answer D.