English and mother tongue pull down a total of 11 marks from average 83. So this means the math and science should compensate this 11 marks.

A) for greatest difference, we want to pull down further with math  so sciences at 90 above will need a bigger value. Lowest math can go is 80. This brings the total pull down to 11 + 3 = 14.

Science needs to be 14 above average of 83  and that would be 97.

Answer, greatest difference is 97 – 80 = 17 #

B) To get smaller difference, we try to bring the score of science closer to math. Either by lowering science to 90 or moving math to 89.

Remember the difference in the marks for math + science and average needs to add up to 11 to compensate the pull down of 11.

i) move science to 90, then math needs to be 87.  Diffence is 3

ii) move math to 89, then science has to be 88. Doesn’t match the table, as science is 90 and above.

Therefore choose i) i. e 3# for answer b)

Note: by ‘pull down’  it’s the difference between the average 83 and the subject score. 

Thank you Ender for the detailed reply!

(a)
83 x 4 = 332
76 + 79 = 155
332 – 155 = 177
177 – 80 – 90 = 7
97 – 80 = 17

(b)
90 – 87 = 3

Ans : (a) 17; (b) 3.

(a)
83 x 4 = 332
76 + 79 = 155
332 – 155 = 177
177 – 80 – 90 = 7
97 – 80 = 17

(b)
90 – 87 = 3

Ans : (a) 17; (b) 3.

Largest Difference = 17

Smallest Difference = 3

Use the average of the 4 to find the sum of the Math & Science marks