Find the Jar with contaminated pills

You have 5 jars of pills. Each pill weighs 10 grams, except for contaminated pills contained in one jar, where each pill weighs 9 grams. Given a scale, how could you tell which jar had the contaminated pills in just one measurement?

Answer:

Take

5 pills from jar 1,

4 pills from jar2,

.... and 

1 pill from jar 5 and 

Put all together on the scale. 

the ideal weight should be (1+2+3+4+5)x10= 150gms. 

For Ex, if the jar2 is contaminated then the weight will be 146 gms. 

so depending on the amount of weight loss we can identify the contaminated jar.