材质：ABS。尺寸：25×21×9cm。内含20把数字锁、20把钥匙。10号锁应该配哪把钥匙呢？几加几会等于10呢？通过配对解锁学习、巩固20以内的加法运算。
Unlock addition skills—with a simple turn of the key! Our self-correcting locks and keys make learning addition facts to 20 a breeze! Kids simply pick a key…solve either one of the two problems printed on it…then find the lock with the answer. If they’ve solved it correctly, the key will turn and the lock will open—for instant reinforcement! Set includes 20 locks and 39 keys; locks measure 3 1/4".
