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Shortcut Methods

Tricks and Shortcuts

1. Binomial Theorem

1. Formula:

$$(a+b)^n=\sum_{r=0}^n {}^nC_r a^{n-r}b^{r}$$

  • (n) choose (r), where (n\ge r), or,

$${}^n C_r=\frac{n!}{r!(n-r)!}$$


2. Binomial Coefficients:

$${}^nC_r= {}^nC_{n-r} $$

$${}^nC_0 = {}^nC_n=1$$

  • If n = 2k, the middle coefficient is

$$= ^{n}C_{k} = \frac {(2k)!} {(k!)^2}$$


##3. Summations/Identities

$$\sum_{i=0}^n {}^nC_i = 2^n$$

$$\sum_{i=0}^n {}^nC_i r^i = (1+r)^n$$

$$\sum_{i=0}^n{}^nC_ir^{n-i}=(1+r)^n$$

  • Product of two Binomials:

$$ (a+b)(c+d) = ac+ad+bc+bd $$

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Shortcut Methods

1. Antibiotic Resistance

  • Percentage rise in antibiotic resistance:

    • Calculate the initial population of bacteria before antibiotic exposure.
    • Count the number of resistant bacteria after antibiotic exposure.
    • Use the formula: % Increase in resistance (%) = ((Number of resistant bacteria - Initial bacterial population) / Initial bacterial population) * 100
  • Rate of mutation:

    • Count the number of resistant bacteria after several generations.
    • Calculate the total number of bacteria after several generations.
    • Use the formula: Rate of mutation (per generation) = (Number of mutations / Total bacterial population)

2. Probiotics and Prebiotics:

  • Minimum daily intake of probiotics:

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