standard costing doubt???

MATERIAL PRICE VARIANCE = ACTUAL QTY USED (STANDARD PRICE - ACTUAL PRICE )

                       -9800 = A.Q. (40 - 42)

                       -9800 = A.Q. (-2)

                    ACTUAL QTY = 4900 KG.

YOU CAN VERIFY THIS ANSWER WITH CALCULATING USAGE VARIANCE :

MAT. USAGE VAR. = STANDARD PRICE (STANDARD QTY - ACTUAL QTY USED )

                                 = 40 ((100*50) - 4900)

                                 =40 (5000 - 4900)

                                = 40 (100)

                                = 4000 (FAVOURABLE)