The isotope 32X (with subscript 15) is phosphorus(32P).The upper number is the Atomic Mass number and the lower is the atomic number.
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480... WITHOUT using a calculator !
First, multiply the top numbers: 32x15=480 Then multiply the bottom numbers 12x12=144 Then put the product of the top numbers of the product of the bottom numbers: 480/144 Then reduce! 10/3
One way is to break the numbers down like this 32x15= 30x10+30x5+2x10+2x5 300+150+20+10=480 That's one way to do it,without really needing a pen and paper or calculator.