This Post Has 9 Comments

    1. The question and answer are correct, but the 3 is a typo. Good catch! You correctly deduced “2009 through 2012” includes 4 years in the set not 3; {2009, 2010, 2011, 2012}. Note that language is different than “between 2009 and 2012” which would not include the end-points and include only the set {2010, 2011}. The answer was calculated using the set of 4 years. We have now changed the problem entirely to refer to a 3 year set which forces students to determine if a leap year falls within the period or not.

  3. You earn 0.5% of what I earn. I earn ?% of what you earn.

    I thought the answer was 200, because of 0.005=5/1000=1/200. the denominator is 200, so that is the answer (the website says it’s wrong, but I want to know why)?

    I read the explanation but I don’t understand it. Why would you take the reciprocal in the first place and why would you multiply that by 100 to get 20000? Please explain.

    1. You have to multiply by 100 because you are expressing the value in percent. The correct answer is the value that equals 200 times expressed as a percent value. 200% is only 2 times. 200 times is 20,000%

  4. Also, for question 40:

    Grandma and Grandpa danced for 20 minutes one day; for each of the next 91 days, they danced for one minute longer than they had on the day before. On those 92 days, they danced for a total of ? minutes.

    I did 92*20=(100-8)20=1840 because of the (20+20+20…+20)+(0+1+2…+91) using the formula: 91*92/2 it would simplify to 91(46) which is 91(50-4)=4186

    (you wouldn’t include 0 in this because it doesn’t make a difference so you don’t multiply by an extra number, only 1-91, which is 91-1=90+1=91 numbers)

    so the total of the minutes Grandma and Grandpa danced would be 1840+4186=6026

    I’m confused because the explanation states you multiply ***91**** by 20, which would give another answer???

    Am I correct? If not, please explain why. Is there a faster method to do this (because I definitely did not solve this in the minute and a half that would be recommended).

    thank you!

    1. Your approach and calculations look correct and agree with the answer provided. I think it is 92 x 20 , not 91 x 20. I think the quickest way is to consider the summation of the arithmetic series from 20 to 111. Sum = Average x Count. The count is 92 terms. The average of a consecutive sequence (or any arithmetic series) is the average of the endpoints: (A1 + An)/2 = (20 + 111)/2. The sum is 131 x (92/2) = 6026.

  5. How do you solve the questions:

    “A chemist claims that he has found a chemical formula that will kill a certain bacteria. He claims it will kill half the bacteria in 40 seconds, and in the next 40 seconds kill half of the remaining half, and so on. If he is correct, and at a certain time there are 30 bacteria still alive, how many bacteria were alive 4 minutes earlier?”

    The 21st century will begin on 1 January 2001. What day of the week will that be?

    Sound travels at about 330 meters per second, but light travels so much faster that it travels almost instantaneously. How long a gap do you expect between seeing the flash and hearing the thunder from a storm 4km away?

    thank youu!! 🙂

  6. oh wait wouldn’t the last question be 4000m/330

    and the first question I tried setting up an equation: 2x/4+x/4… I don’t know how to continue, PLEASE help me

    I don’t knoww

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Back To Top