In the normal approximation to the binomial,

Probability of getting head p = 0.5

Probability of getting tail = 1-0.5 = 0.5

mean=np=20*.5=10

SD=sqrt [npq]=sqrt[10*0.5]=2.236

z value for 14 heads=[14 -10]/2.236=1.789

looking up a z table you will get

P(10<x< 14] = 0.4632 or 46.32 %

ans: 0.4632 or 46.32 %

Probability of getting head p = 0.5

Probability of getting tail = 1-0.5 = 0.5

mean=np=20*.5=10

SD=sqrt [npq]=sqrt[10*0.5]=2.236

z value for 14 heads=[14 -10]/2.236=1.789

looking up a z table you will get

P(10<x< 14] = 0.4632 or 46.32 %

ans: 0.4632 or 46.32 %