-2 5*24*-4

Dear Riyaz,
Here is the solution:
(-25) x 24 x (-4)
= 24 x (-25) x (-4)
= {24 x (-25)} x (-4) 
= 24 x {(-25) x(-4)}      --- [As {a x b} x c = a x {b x c} - Associative property]
= 24 x {100}
= 2400 --- (ANS.)

Hope it helps! 
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Cheers!