Question

The following table gives the lifetimes of $400$ neon lamps: How many lamps have a lifetime of more than$700$ hours?

Life Time (in hours)	Number of lamps
300 – 400	14
400 – 500	56
500 – 600	60
600 – 700	86
700 – 800	74
800 – 900	62
900 – 1000	48

Answer 1

Given:

The lifetimes of $400$ neon lamps

Numbers of neon lamps having their lifetime more than $700=$No. of neon lamps having their lifetime as $700-1000$

$=$ No. of neon lamps having their lifetime ($700-800$) $+$ No. of neon lamps having their lifetime $800-900+$ No. of neon lamps having their lifetime $900-1000\mathrm{hrs}$.

$=74+62+48=184$

Hence, numbers of neon lamps having their lifetime more than $700=184$.