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Mathematics: Post your doubts here!
(iii) To ensure at least one woman chosen, first step is to choose 1 from 3 women, which is 3C1.Then randomly choose the other 2 from the remaining 8 people. Overall it is 3C1 × 8C2 = 84 -
Mathematics: Post your doubts here!
It can be decoded by copying it to the reply zone and choose a normal font for them. :p The deciphered text: :D -
Chemistry P4| A2 only
There was another question paper also asking for the shape of d-orbitals of metal cation in a complex ion. I know that three of them are on lower energy level and the other two on higher. The normal shape of even-energy d-orbitals... I heard someone said they are like double-dumbbells. -
Mathematics: Post your doubts here!
For god's sake what is this font? :D It doesn't seem to be from XPF font family. Is it a Windows Font? -
Mathematics: Post your doubts here!
Because the number 5 is taken by the first digit. That is, there is only one choice for the first digit. Then there are three digits left for he remaining five numbers to fit in. -
Physics: Post your doubts here!
My pleasure. That is indeed a question with depth. ;) -
Mathematics: Post your doubts here!
Be aware that no digits are repeated. Between 5000 and 6000, so the first digit is definitely 5. 5 is used, five numbers remaining, then it's permutation 5P3. 1 × 5P3 = 60. -
Physics: Post your doubts here!
(1)Electric field lines point from positive side towards negative side, so P experiences a rightward force while N a leftward force. (2)Torque is a kind of moment. It is the moment of a couple. Here the forces on two charges form a perfect couple. The formula for torque (T): T = F d [d =... -
Chemistry: Post your doubts here!
I remember that in IGCSE Chemistry textbook the ions consisting of groups of atoms are called molecular ions, like SO4(2-), CO3(2-), NO3(-) and NH4(+). The complex ion is quite similar. Or should we call it "multi-molecular ion"? :p (Just kidding) -
Chemistry: Post your doubts here!
No, it's totally irrelevant. What determines the chiral centre are four groups with different atoms or structures, not with different relative charges. Mole of Ca or mole of H2. In fact, the equation must first be stoichiometrically balanced (balanced to smallest possible integers), and then... -
Chemistry: Post your doubts here!
Maybe molecular ion formed by metal cation bound to ligands? :P That's my own words... -
Physics: Post your doubts here!
It is not x to be differentiated but Ep (potential energy) to be, with respect to x. Think about the relationship between velocity and displacement. Velocity is defined as the rate (rapidness) of change of displacement, or dx/dt. Here the rate of change is in terms of time. So it's dx/dt... -
Physics: Post your doubts here!
The diagram can be drawn using the Parallelogram Rule. To find the resultant magnitude, there are two ways: - you have a rule don't you? Use it to measure the relative length of the forces. Force magnitude ratio equals diagram length ratio. Use the ratio to calculate. This is the... -
Physics: Post your doubts here!
x = distance from the centre. Work done is equal to force × distance, this is the formula. :p In fact, when force changes with distance (a function of distance), the work should be calculated by integrating force × dx. On a force-against-distance diagram, the area under the line/curve is work... -
Mathematics: Post your doubts here!
ARRRGH, huge mistake I've made... The question stated "with replacement" which means each time pick one out and put it back before picking again. I did not notice this, BIG sorry about that. :P Yeah (a) is (52C1)^8, each time choosing 1 from 52 for 8 times, that is just 52^8 = 5.346E^13. The... -
Mathematics: Post your doubts here!
Are you sure that for (a) the answer is 5.346E^13 ? Choosing 8 from 52, sequence included, so that is permutation, 52P8, and I got 3.034E^13. For (b) I also got a different result. The procedure is like choosing 3 from 12, 3 from 20 and 2 from 20, then put them in sequence. So it's first... -
Physics: Post your doubts here!
Not I, not you, not anyone. Decay starts by itself. It does not need a particular action as trigger. Once the nuclei have enough energy or are unstable enough, they begin decay on their own. -
Chemistry: Post your doubts here!
Once you find a carbon atom that is connected to four groups different from each other, that carbon atom is a chiral centre. Carbon connected to only three or even two groups cannot be a chiral centre. In a moderately complex molecule, there could be more than one chiral centre. :) -
Further Mathematics: Post your doubts here!
Well, further maths does not need how fast you can finish a-level maths. It requires a knowledge foundation, a certain knowledge level, which can be fully covered by a-level maths. So as long as you have mastered a-level, you can start doing further maths.