hai to cung lam 1 cong viec . Neu lam rieng thi to A can 20 gio , to B can can 15 gio moi lam xong . Nguoi ta giao cho to A lam trong 1 thoi gian roi nghi va to B lam tiep cho xong. Biet thoi gian to A lam it hon to B la 3 gio 20 phut. Tinh thoi gian moi to da lam

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