# Microscope converging lens problem

1. Nov 17, 2015

### FritoTaco

1. The problem statement, all variables and given/known data
A microscope slide is placed in front of a converging lens with a focal length of 2.44 cm. The lens forms an image of the slide 12.9 cm from the slide.

a. How far is the lens from the slide if the image is real?

2. Relevant equations
1/f = 1/di + 1/do The real equation (but harder in my opinion to read) is 1/p + 1/q = 1/f

3. The attempt at a solution
I know that if the image is real, focal length is positive on a converging lens (negative focal length for a diverging lens). I plugged 2.44cm into f and 12.9 into di. The problem is, I need a common denominator in this;
1/2.44 = 1/12.9 + 1/do. I can't find a least common multiple for 12.9 and 2.44. I tried to switched centimeters into millimeters and got 129mm and 24.4mm. This doesn't work because there's still a decimal in di (24.4mm). I don't know where to go from here because I'm use to using whole numbers but not decimals.

2. Nov 17, 2015

### ehild

2.44 and 12.9 are not integers. Use their product as common denominator.

3. Nov 18, 2015

### FritoTaco

Hey, it helped me a lot, thank you! I solved the problem correctly.

4. Nov 18, 2015

Well done!