Aptitude Discussion

Q. |
A set of S consists of, i). All odd numbers from 1 to 55. What is the index of the highest power of 3 in the product of all the elements of the set $S$? |

✔ A. |
35 |

✖ B. |
48 |

✖ C. |
6 |

✖ D. |
36 |

**Solution:**

Option(**A**) is correct

The product of all element of $S$ is:

$\{3, 5, 7, 56, 58, 60$

$9, 11, 13, 62, 64, 66$

………………………

………………………

$51, 53, 55, 146, 148, 150 \}$

⇒ $\{ 3, 3×3, 3×5, .................3×17$

$3×20, 3×22, 3×24, ……………..(3×50)M\}$

⇒ $3^9×3×9×3×3^{16}×24×30×36×42×148N$

⇒ $3^{35}S$

**Aalok**

*()
*

3,9,15,21,27,33,39,45,51 contains 9 3's and $9=3^2$, $27=3^3$ contains extra $1+2=3$ 3's

$9+3=12$ odd number multiples of 3 are there not 13

similarly 23 not 24

so ans $=12+23=35$

i think 37 would be answer . because b/w 1 to 55 there are 13 odd number which are multiple of 3.

$3,9,15,21,27,33,39,45,51$. where as $9 = 3^2$, $27= 3^3.$

And there are 24 number of 3 exist b/w 56 to 150

$60, 66,72,78,84,90,96,102,108,114,120,126,132,138,144,150$. where as $72 = 3^2*8$, $90=3^3*10$, $108 = 3^3*4$, $126 = 3^2*14$, $144 = 3^2 * 16$.

so $13+24 = 37$.

please reply if i am wrong.