Extending 3-month Math Guide Online subscriptions

In light of yesterday’s announcement by the College Board that the June SAT is canceled, I am extending all current 3-month subscriptions to the Math Guide Online through August 29 (the date of the August SAT). New 3-month subscriptions purchased between now and May 29 will also be extended through the August date. Stay safe (more…)

Try the Math Guide Online for free

UPDATE: Now you can sign up for trial access (3 days) to the whole Math Guide Online. A bunch of folks have asked me if there’s a free trial for the new Math Guide Online. Well, at launch there wasn’t but now there is! Click above. If you’re ready to purchase access to the whole (more…)

In a certain class of 70 students, 4/7 of the students are boys, and the ratio of students 10 years or older to students less than 10 years is 2:3. If 2/3 of the girls are less than 10 years old, how many boys are 10 years old or older?

OK, so you have 40 boys and 30 girls. That’s easy enough to calculate because you’re given a part:whole ratio (boys to total students) and you already know the total number of students is 70. Be careful about the second ratio, though, because it’s a part:part ratio! If the ratio of older to younger is (more…)

The polygon ABCDEFGHI is a regular 9-sided polygon with consecutive vertices labeled in alphabetical order. What is the measure of angle ACE?

OK, so when you have a regular n-gon, you can figure out each angle in it using this formula: [(n-2)180]/n. In this case, 7*180/9 = 140, so we know each angle in the polygon is 140°. I couldn’t draw this quickly on the computer I’m on, so I found a good n-gon picture to mark (more…)