=IF(A1<10,A1*2,IF(A1>=10<=20,A1*3,IF(A1>20,A1*5)))
b1 =if(a1<10,a1*2,if(a1<=20,a1*3,a1*5))
=LOOKUP(A1,{0,10,21},A1*{2,3,5})
b1=lookup(a1,{0,10,20},a1*{2,3,5})