Question

If 3 is subtracted from each of the first 11 multiples of 5, then find the ratio of the new mean to the old mean.

• A. 9 : 11
• B. 9 : 10
• C. 10 : 9
• D. 5 : 4

Answer 1

The correct option is D 5 : 4

The first 11 multiples of 5 are
5, 10, 15, 20, 25, 30, 35, 40, 45, 50 and 55.

Old Mean
$=\frac{5+10+15+20+25+30+35+40+45+50+55}{11}$
$=\frac{330}{11}$
$=30$

Sum of the 11 multiples of 5 when 3 is subtracted from each is
$=(5-3)+(10-3)+\dots \dots +(55-3)$
$=(5+....+55)-3\times 11$
$=330-33=297$

New mean $=\frac{297}{11}=27$

Thus, ratio of the new mean to the old mean
= 27 : 30
= 9 : 10