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2 rocks

Step-by-step explanation:

2 crates + 2 rocks = 1 crate + 4 rocks

2 crates + 2 rocks = 2 crates + 8 rocks

Hence, 1 crate = (8-4)÷2

= 2 rocks

21

step-by-step explanation:

explanation:

infrared radiation has wavelength in the range between 700 nm and 1 mm. lets' convert these values into scientific notation, keeping in mind that:

let's start from the lower value, we have:

(we moved the dot two places to the left, so we increased the exponent by 2 units, from -9 to -7)

the higher value is:

so, the range of wavelength of infrared radiation is: