按照以下步骤可推算出两种棋都不会下的人有17人。
1、已知三二班有学生45人，如下图，
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https://iknow-pic.cdn.bcebos.com/a8773912b31bb051efc66380387adab44bede0bc"/>
2、45人中有会下象棋的人21人，如下图，
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https://iknow-pic.cdn.bcebos.com/0df3d7ca7bcb0a46a2cd5b916563f6246a60afaf"/>
3、45人中会下围棋的有17人，如下图，
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https://iknow-pic.cdn.bcebos.com/3ac79f3df8dcd1006a4928897c8b4710b8122f45"/>
4、班上共45人，这些人既会下象棋又会下围棋的人有10人，那么就将会两种棋艺的同学同框，如下图，
/iknow-pic.cdn.bcebos.com/1b4c510fd9f9d72a3cb7c0b5da2a2834359bbb43"target="_blank"title="点击查看大图"class="ikqb_img_alink">/iknow-pic.cdn.bcebos.com/1b4c510fd9f9d72a3cb7c0b5da2a2834359bbb43?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto"esrc="
https://iknow-pic.cdn.bcebos.com/1b4c510fd9f9d72a3cb7c0b5da2a2834359bbb43"/>
5、剩下的同学两种棋都不会下的人数为17人，如下图。
/iknow-pic.cdn.bcebos.com/d62a6059252dd42a77c0d1030d3b5bb5c8eab849"target="_blank"title="点击查看大图"class="ikqb_img_alink">/iknow-pic.cdn.bcebos.com/d62a6059252dd42a77c0d1030d3b5bb5c8eab849?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto"esrc="
https://iknow-pic.cdn.bcebos.com/d62a6059252dd42a77c0d1030d3b5bb5c8eab849"/>