小丁丁有13本书，送掉7本，还剩几本书？

14－{#blank#}1{#/blank#}=5          17－{#blank#}2{#/blank#}= 8

5＋{#blank#}3{#/blank#}=10          7＋{#blank#}4{#/blank#}=16

{#blank#}1{#/blank#}＋6＝10       9＋{#blank#}2{#/blank#}＝15       5＋{#blank#}3{#/blank#}＝15

{#blank#}4{#/blank#}＋10＝12      7＋{#blank#}5{#/blank#}＝13       8＋{#blank#}6{#/blank#}＝16

11-9=      14-5=      16-9=       16-7=       11-6=

15-8=      13-6=      11-2=       16-8=       14-6=

17-8=      15-9=      13-8=       15-6=       14-9=