If w = 20 and t = 40 have been rounded to the nearest 10 find the upper bound of $$w\times t$$ .

If h = 9.9 and g = 8.8 have been rounded to 1 decimal place find the upper bound of $$h\times g$$ .

If u = 22.4 and z = 86.5 have been rounded to 3 significant figures find the upper bound of u + z.

If r = 9.8 and m = 6.8 have been rounded to 2 significant figures, find the lower bound of $$r\times m$$ .

If a = 9300 and k = 5200 have been rounded to 2 significant figures find the lower bound of a + k.

If g = 8.44 and p = 9.90 have been rounded to 3 significant figures find the upper bound of $$g\times p$$ .