Trjtdtk

I want to write this equation in LaTeX:

This my LaTeX code for the equation:

beginequation nonumber
 q^*_1 =fractextnumber of women who had their second birth in 1971textnumber of women who had their first birth in 1970 textbf- number of women had their second birth in 1970
 end equation

How can write the denominator as given in the picture?

A simple way is to use array for the denominator

beginequation nonumber
 q^*_1 =fractextnumber of women who had their second birth in 1971
 beginarrayc
 textnumber of women who had\
 texttheir first birth in 1970 
 endarray
 -
 beginarrayc
 textnumber of women who had\
 texttheir second birth in 1970 
 endarray
 
 endequation 

I'd define a suitable notation, avoiding long verbal descriptions. I also added the verbose version, but adding parentheses for clarity.

documentclassarticle
usepackageamsmath

begindocument

Let's denote by $W(n,y)$ the number of women who had their $n$th~birth
in the year~$y$. Then
beginequation*
q^*_1 = fracW(2,1971)W(1,1970)-W(2,1970)
endequation*
We can also typeset this with words, but it comes out quite awful
unless we add parentheses
beginequation*
q^*_1 =
frac
 textnumber of women who had their second birth in 1971

 Bigl(
 begintabularc
 number of women who had \
 their first birth in 1970
 endtabular
 Bigr)
 -
 Bigl(
 begintabularc
 number of women who had \
 their second birth in 1970
 endtabular
 Bigr)

endequation*

enddocument

Using equation* avoids the need for nonumber.

An approach with parbox

documentclassarticle
usepackageamsmath
begindocument


beginequation nonumber
 q^*_1 =fractextnumber of women who had their second birth in 1971textparbox4.5cmcentering number of women who had their first birth in 1970 - textparbox4cmcentering number of women had their second birth in 1970
 end equation 

enddocument

Of course the lengths could be different to fit your sizes...

Just to throw in an alternative layman's view

documentclassstandalone
usepackageamsmath
begindocumenthuge
$q^*_1 = textnumber of women who had their ( frac 2^ndtext birth in 1971 1^sttext birth in 1970~-~ 2^ndtext birth in 1970$)
enddocument

Here is a competety different approach using variables instead of the text:

documentclassarticle
usepackageamsmath

begindocument
beginalign*
 q^*_1 &=fracAB-C \
 textwhere~A &= textnumber of women who had their second birth in 1971 \
 B &= textnumber of women who had their first birth in 1970 \
 C &= textnumber of women who had their second birth in 1970 \
endalign* 
enddocument

For a horizontally centered equation one could use something like the following:

documentclassarticle
usepackageamsmath

begindocument

beginequation
 q^*_1 =fracAB-C nonumber
endequation 
beginalign*
 textwhere~A &= textnumber of women who had their second birth in 1971 \
 B &= textnumber of women who had their first birth in 1970 \
 C &= textnumber of women who had their second birth in 1970 \
endalign*
enddocument