Question

A rectangular plate has a length of (21.3 ± 0.2) cm and a width of (9.80 ± 0.10) cm. Calculate the area of the plate and also the percentage error.

Answer 1

ᴀʀᴇᴀ ᴏꜰ ᴛʜᴇ ʀᴇᴄᴛᴀɴɢʟᴇ = ʟᴇɴɢᴛʜ  x  ᴡɪᴅᴛʜ

ᴡᴇ ᴡɪʟʟ ᴄᴀʟᴄᴜʟᴀᴛᴇ ᴛʜᴇ ᴘᴇʀᴄᴇɴᴛᴀɢᴇ ᴏꜰ ᴜɴᴄᴇʀᴛᴀɪɴᴛɪᴇꜱ. 

ꜰᴏʀ ᴀ ʟᴇɴɢᴛʜ: ᴘ 1 = ( 0.2 · 100 ) : 22.4 = 20 : 22.4 = 0.893

ꜰᴏʀ ᴀ ᴡɪᴅᴛʜ: ᴘ 2 =  ( 0.1  · 100 ) : 8.4 = 10 : 8.4 = 1.190

ᴘ 1 + ᴘ 2 = 0.893 + 1.190 = 2.083 %

ᴀ = 22.4 · 8.4 = 188.16 +/-  2.083 %

 ᴜɴᴄᴇʀᴛᴀɪɴᴛʏ: 188.16 · 0.02083  = 3.92 

ᴀ = 188.16 +/- 3.92 ᴄᴍ²