Multiplying numbers with different signs

Find the product 4 x ( -5 ) x ( - 7.5) Just multiply 3 numbers here, some are positive some are negative. We can do it in any order Lets start with 4 x -5, and then we will multiply what ever we get with - 7.5 so lets write it again 4 x ( -5 ) x ( - 7.5) The first thing we need to realise is a (+) x (+) = +, and a (+) x( -) = - or (-) x (+) = - (- ) x ( -) = +. If we multiply two numbers with same sign, we get a + answer and if we multiply two numbers with different sign we get a - answer.4 x 5 = 20 we have a (+) x (-) ,two numbers with different sign so we will have a - it becomes -20 x - 7.5. we will figure what that is, I will work out what is 20 x 7.5 = 150.0 now we think if it is + or - we have a (-) x (-), they are the same sign the answer will be +. so the answer is + 150.0