21 brain games guaranteed to boost your brain power

Kate and Faizal both believe that they need a cup of coffee every three hours to stay awake and function. They both drink their first cup at 8am and another one every three hours 
thereafter until they go to sleep. Considering the following facts, who is spending more on coffee each week?

Kate stays up until 10pm Sunday through Thursday and until midnight on Friday and 
Saturday. Faizal stays up until 10pm every day.

Kate pays $3 per cup of coffee. Faizal drinks higher-grade organic coffee and pays $4 per cup.

Faizal. He spends $140 per week, while Kate spends $111

You just bought nine beautiful lakeside campsites, which you can rent to campers with tents for $20 per campsite per night. You can also upgrade the sites with electrical hookups. This will cost you $60 per campsite but will allow you to rent to RVers for $40 per night. Suppose you can always fill your campground to capacity. If you’re starting without any cash on hand, how many nights will pass before you’ll be able to upgrade all nine sites?

Three. On the first night, you’ll host nine tents and make $180, which you’ll use to upgrade three sites. On the second night, you’ll host three RVs and six tents, earning $240, letting you upgrade another four sites. On the third night, you’ll host seven RVs and two tents, earning you more than enough to upgrade the last two.

Rich lives in the Eastern Standard Time zone. His sister, Barbara, lives in the Central European Time zone, six hours ahead of him. Rich works between 8am and 5pm in his local time and goes to sleep each evening at 10 pm on the dot. Barbara works between 9am and 6pm and always goes to sleep at 11.30 pm in her own local time.

Is there any window in which Rich could call Barbara after his workday without interrupting her on the job or disturbing her sleep?

Yes, between 5 and 5.30pm EST.

Can you find the doll among all these Christmas presents?

Each letter from A through H has one of the 8 values listed below, and no two letters have the same value. Which number goes with which letter to make all the equations true?

2 3 4 5 8 12 13 17

F + A = C
G + B = D
F + D = H
B + H = C
E + G = B

A = 13, B = 5, C = 17, D = 8, 
E = 2, F = 4, G = 3, H = 12.

Place one of the four basic arithmetic operations (+, –, ×, ÷) 
in each box to make a correct equation. All operations are performed from left to right, ignoring the mathematical order of operations. The result 
at each step must be a positive whole number. What’s the equation?