the r+1 th term in the expansion is C(10,r) * 5^(r/5) * 2^(5-r/2).
so, 2 divides r, 5 divides r, 10 divides r. so r = 0,10.
there are two such terms.
answer is 6 isnt it ?? coz u get rational terms only if u put r=0,2,4,6,8,10 hence no of rational terms is 6.