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# GMAT: Math 7

36-41, pgs. 156-157. Created by Sal Khan.

## Want to join the conversation?

• #41 answer = 2/5 am i not correct?
• For #37, why is the answer II only? I'm struggling to understand how that is answer he arrived at.
• As Sal demonstrated, if a number is divisible by both 5 and 7, then it will be divisible by 35 * some factor (he used k in the video). So to meet the requirement, 35 is the only answer the question. For example, 105 is divisible by both 5 and 7, as well as, 35. However, 105 is not divisible by 70 so that answer does not work. I would be interested to see what the answer key in the book actually says.
• Can someone explain why on question 37 III. 70 is not correct?
• We are told that the mystery integer is positive and is divisible by both 5 and 7. So, it `could` be
35, 70, 105, 140, 175, 210, and so on.
But of this list, only every other number is divisible by 70. So 70 CANNOT be correct.

In order for the mystery integer to ALSO be divisible by 70, we would have to be told that the mystery integer is ALSO divisible by 2, in addition to being divisible by 5 and 7--and they didn't say that. That chops out 70 as a possible answer.
• is there a text book for this?
(1 vote)
• Yes. Go to the very first gmat math video. Someone posted a link to download the pdf. You can also buy the book.
• Q41: 2=5t
t=2/5 ( how can it be 5/2?)
• At around the mark in question 38, why did Sal do b - 4 = 3? The 3 came from 3x but how did Sal know to do that?