Aptitude Discussion

Q. |
If $b$ equals 10% of $a$ and $c$ equals 20% of $b$, then which one of the following equals 30% of $c$? |

✖ A. |
$0.006\% \text{ of } a$ |

✖ B. |
$0.006\% \text{ of } a$ |

✖ C. |
$0.06\% \text{ of } a$ |

✔ D. |
$0.6\% \text{ of } a$ |

**Solution:**

Option(**D**) is correct

$b = 10\%$ of $a = (\dfrac{10}{100})×a = 0.1a$

$c = 20\%$ of $b = (\dfrac{20}{100})×b$

$= 0.2b = {0.2}×{0.1a}$

Now, 30% of $c = (\dfrac{30}{100})×c$

$= 0.3c = (0.3)(0.2)(0.1a)$

$= 0.006a = 0.6\%a$

Thus, correct choice is option(D).

**Edit:** Thank you **Ravi**, based on your input, options have been modified.

**Arun**

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**Naaz**

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$b= 10\% * a$ $= (\frac{10}{100})*a$ $= 0.1*a$.........eqn(1)

similarly,

$c= 20\% * b$ $= (\frac{20}{100})*b$ $= 0.2*b$.......eqn(2)

Let $30\%$ of $c = x$

$x = 30\% * c$ $= (\frac{30}{100})*c$ $= 0.3*c$.........eqn(3)

Now substitute value of $c$ i.e, equation(2) in eqn (3)

$x = 0.3 *(0.2*b)$

now substitute value of $b$ i.e, eqn (1) in above equation

$x = 0.3 *(0.2 * 0.1*a)$

hence,

$x= 0.6a$ :)

You have done everything right until the last step.

$x = 0.3 *(0.2 * 0.1*a)$ gives $x = 0.006a$ and NOT $0.6a$

**Ravi**

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I guess you need to modify the options to compare it with either $a$ or $b$.

Updated, thank you for letting me know about this.

**Navya**

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how it become 0.6a =40%

They doesn't asked percentage. They just asked only 30% of c=? that's all, so the ans is 0.006 of a