Write the following in correct mathematical language: 45.23

Forty-five and twenty-three hundredths.

In general, with decimals, the first place value after the decimal is read as a tenth, the second is read as a hundredth, the third is read as a thousandth, and so on. In front of the decimal, we know that 4 is in the tens place and 5 is in the ones place, so we say forty-five. Past the decimal, 2 is in the tenths place (think about how 2/10 = .2, which is "two-tenths") and 3 is in the hundredths place (think about how 23/100 = .23). You read the number after the decimal like normal ("twenty-three," "two-hundred fifteen," etc), then you add the place ("tenths, hundredths, ten-thousands") at the very end.