Questions

Yes, you are requested to write an essay as part of your TOEFL iBT exam. There are 5 major types for TOEFL essay topics. They are:

1. Agree or Disagree

2. Preference

3. Description / Explanation

4. If / Imaginary

5. Compare & Contrast

The best way to prepare for this essay writing is to understand the writing style clearly. To understand the the genre, you can refer some sample essays submitted before by different contestants. You can get such sample TOEFL essays from various sources such as TOEFL training websites, cheap essay writing service sites, online libraries, etc. Once you are well aware of the writing pattern the next thing is to practice writing random essays. Keep in mind that you should practice writing essays of all above mentioned 5 types. If you make it a routine to write random essays, gradually you can compete at higher level to write the given essay topic for your TOEFL iBT exam.

At least one black can be chosen in two ways from each box:
Now, probability of choosing at least one black ball from first box 

= 1/2 × [ (2C1× 2C1)/4C2 + 2C2/ 4C2 ]= 5/12

Probability of choosing at least one black ball from 2nd box
= 1/2 × [(4C1×12C1)/16C2 + 4C2/ 16C2] = 9/40

Final probability

= 5/12 + 9/40 = (50 + 27)/120 = 77/120

Siphon is a tube bent to form two legs of unequal length by which a liquid can be transferred from a reservoir and then down to a lower level of it.

Siphon will fail to work if, the level of the liquid in the two vessels are at the same height.