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A2 Physics | Post your doubts here
Use the formula Xc = Vo / Io. Since this is a division. Percentage uncertainty is required. Convert the absolute uncertainties of Vo and Io all to percentage uncertainties (Absolute unc. value divided by measured value), then add them up each row. The sum is the percentage unc. of Xc. To get... -
Chemistry P4| A2 only
By comparing 1 and 2, we get [CH3CHO] is 1st order. By comparing 2 and 3, we get [CH3OH] is 1st order. Then by comparing 1 and 4: [CH3OH] becomes twice large, so does [H+]. We already know that [CH3OH] is 1st order, so it being twice large shall double the rate. But actually, the rate... -
Chemistry P4| A2 only
Sorry but which question do you mean? Is it the one talking about Pb(II) and PB(IV) ? -
Chemistry P4| A2 only
Electrolytic cell is the other way around. The positive electrode attracts negative ions, or anions. Since the positive electrode loves electrons, it can "grab" electrons from anions. Once the anions lose electrons they get oxidised. So the positive electrode is the anode. The negative... -
Chemistry P4| A2 only
Okay here's the point: Anode is NOT defined as the positive electrode. Instead, it is the electrode where OXIDATION takes place. In the Zn-Mg cell you mentioned, yes because Mg has a more negative E(red) it gets oxidised so the Mg electrode is the anode. Think it this way: the electrode... -
Chemistry P4| A2 only
As in (i) you get the orders all 1. So the formula is rate = k[CH3CHO][CH3OH][H+] According to number 1 experiment, k × 0.20 × 0.10 × 0.05 = 1.00, k × 0.001 = 1.00, k = 1000 then when all concentrations are 0.20, rate = 1000 × 0.20 × 0.20 × 0.20 = 8.00 -
Chemistry P4| A2 only
Well, be careful here: where E(red) is MORE NEGATIVE is the ANODE. The anode always has the oxidation reaction taking place and that's why it is called the anode. Surely in the cell electron flows from it to the other electrode so that it is the negative electrode, but it is still the anode... -
Further Mathematics: Post your doubts here!
Of course you will. :D -
Chemistry P4| A2 only
(b) Phenylamine, like phenol, can be involved in electrophilic substitution with bromine. The product, 2,4,6-tribromo-phenylamine, is also a white precipitate. So the test can be carried out using bromine water. Phenylamine reacts to decolourise the solution and form a white ppt. while... -
Chemistry P4| A2 only
Here they don't need to form dative covalent bonds. Chlorine atoms each have a lone electron. They prefer to donate that one to form covalent bonds with one from carbon. The reaction equation: CCl2 + H2O = CO + 2HCl -
Mathematics: Post your doubts here!
My pleasure. :) There are certain tricks in solving P & C questions. The pattern is always given some subjects (people, trees, books, cards, letters etc) and slots (seats, places...), each part of the question introducing some restrictions on some of the subjects (such as which two/three letters... -
Mathematics: Post your doubts here!
If two events (say Q and R) are independent, then: - P(Q&R) = P(Q) × P(R) From this, we can derive that - P(Q|R) = P(Q|R') = P(Q) - P(R|Q) = P(R|Q') = P(R) If any of the three is fulfilled, the two events must be independent. A & B: If A happens, the first throw needs to be 1 for the sum... -
Mathematics: Post your doubts here!
The (i) part is always the most direct in all P & C questions :D 14P12 = 4.36E^10 (ii) -The 3 seats on the right are taken by the 3 businessmen. So first it's 3P3. -Then the Lins sit in a row on the same side of the aisle, the available locations could only be the 3 pairs of seats on the upper... -
Mathematics: Post your doubts here!
Oops... I didn't notice the "probability" AGAIN. (I lost some marks in the Mock due to this. :P) Really sorry about that dude. For (b), the probability is 70560 / 362880 = 7/36. And for (c)... Well I guess I skipped directly to (d) just now. :P (c) doesn't need to concern about the magnolias... -
Mathematics: Post your doubts here!
(a) Simply 9! = 362880 (b) Regard the two trees as a unit. There are 7 locations available to place this unit. (Any two neighbouring slots can form a valid location but not on different sides.) 7 locations for 1 unit to fit in, that's 7P1. Next, there are 7 slots left (9 minus 2) for the... -
Mathematics: Post your doubts here!
7(i) Total number of choices = 12C3 number of choices with all different colours = 5C1 × 4C1 × 3C1 probability = 5C1 × 4C1 × 3C1 / 12C3 = 3/11 7(ii) Question says "exactly two" so it's taking 2 from the 4 green, and the other 1 from remaining 8 peppers. probability = 4C2 × 8C1 / 12C3 = 12/55... -
Mathematics: Post your doubts here!
In the case, it is impossible to have two numbers that can both be greater than 8 and at the same time multiply to get 24. This means the possibility that the two events both happen is zero. So they are mutually exculsive. -
Mathematics: Post your doubts here!
2(i) Let's say attending the training session is event A, and chosen for the team is event B. You can see P(A) = 0.5, P(B|A) = 1 and P(B|A') = 0.6 So P(B) = 0.5 × 1 + 0.5 × 0.6 = 0.8 2(ii) P(A&B) = P(B|A) × P(A) = 1 × 0.5 = 0.5 P(A|B) = P(A&B) / P(B) = 0.5 / 0.8 = 0.625 -
Mathematics: Post your doubts here!
Yeah you're right. My answer involves some permutations. :P -
Mathematics: Post your doubts here!
Mutually exclusive means two events cannot both happen, which can be represented by P(A&B) = P(A|B) = P(B|A) = 0.