Mental Math Practices on Ratio, Percents and Proportion

Mental Math Practices: All questions can be solved in your head reasonably fast (less than 5 minutes) if you understand the concepts well.

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1. What is 12.5% of 128?

2. After 20% discount, you paid $144? What is the original price?

3. To make 20% profit, you charge your customer 144 dollars. What is the wholesale price?

4. You lost 20% in the stock market. What percentage increase will you break even?

5. A : B = 2 : 5 and A is 75 more than B, what is B?

6. A : B = 2 : 3 and A + B = 14, what is A and what is B?

7. A : B = 3 : 5 and B : C = 2 to 9, what is A : B?

8. Two triangles are similar and the length of their base ratio is 1: 2. The smaller triangle has a base that equals 5 and an area that is 110. What is the area of the larger triangle?

9. One side of the square increases 10% and the other side decreases 20 percent. What is the percentage change? Increase or decrease? By how much?

10. There are 60 students in a gym and 30% are boys. After a few more boys enter the gym, now 40% are boys. How many boys enter the room?