Answer:
1. Use bodmas:
7 + 0.2 + 0.07 + 0.008 = 7.278
Tip when multiplicating by numbers like 0.1 (1/10), 0.01 (1/100), and 0.001 (1/1000):
When you multiplicate numbers by numbers like i said just move comma. For example:
7 * 0.1 = 0.7 (so u moved from 7 to .7)
7 * 0.01 = 0.07 (bc u moved to .07)
7 * 0.001 = 0.007 (bc u moved to 0.007)
Also u can multiplicate 1 by 7, and write zeros before 1
7 * 0.1 = 0.7 (0 because you copied, and 7, because 1*7 = 7)